NASA’s next planet-hunter, the Transiting Exoplanet Survey Satellite (TESS), successfully launched on a SpaceX Falcon 9 on April 18, 2018. TESS will search for new worlds outside our solar system for further study. Credits: NASA Television
NASA’s Transiting Exoplanet Survey Satellite (TESS) launched on the first-of-its-kind mission to find worlds beyond our solar system, including some that could support life.
TESS, which is expected to find thousands of new exoplanets orbiting nearby stars, lifted off at 6:51 p.m. EDT Wednesday on a SpaceX Falcon 9 rocket from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida. At 7:53 p.m., the twin solar arrays that will power the spacecraft successfully deployed.
“We are thrilled TESS is on its way to help us discover worlds we have yet to imagine, worlds that could possibly be habitable, or harbor life,” said Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate in Washington. “With missions like the James Webb Space Telescope to help us study the details of these planets, we are ever the closer to discovering whether we are alone in the universe.”
Over the course of several weeks, TESS will use six thruster burns to travel in a series of progressively elongated orbits to reach the Moon, which will provide a gravitational assist so that TESS can transfer into its 13.7-day final science orbit around Earth. After approximately 60 days of check-out and instrument testing, the spacecraft will begin its work.
“One critical piece for the science return of TESS is the high data rate associated with its orbit,” said George Ricker, TESS principal investigator at the Massachusetts Institute of Technology’s (MIT) Kavli Institute for Astrophysics and Space Research in Cambridge. “Each time the spacecraft passes close to Earth, it will transmit full-frame images taken with the cameras. That’s one of the unique things TESS brings that was not possible before.”
For this two-year survey mission, scientists divided the sky into 26 sectors. TESS will use four unique wide-field cameras to map 13 sectors encompassing the southern sky during its first year of observations and 13 sectors of the northern sky during the second year, altogether covering 85 percent of the sky.
TESS will be watching for phenomena called transits. A transit occurs when a planet passes in front of its star from the observer’s perspective, causing a periodic and regular dip in the star’s brightness. More than 78 percent of the approximately 3,700 confirmed exoplanets have been found using transits.
NASA’s Kepler spacecraft found more than 2,600 exoplanets, most orbiting faint stars between 300 and 3,000 light-years from Earth, using this same method of watching for transits. TESS will focus on stars between 30 and 300 light-years away and 30 to 100 times brighter than Kepler’s targets.
The brightness of these target stars will allow researchers to use spectroscopy, the study of the absorption and emission of light, to determine a planet’s mass, density and atmospheric composition. Water, and other key molecules, in its atmosphere can give us hints about a planets’ capacity to harbor life.
“The targets TESS finds are going to be fantastic subjects for research for decades to come,” said Stephen Rinehart, TESS project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s the beginning of a new era of exoplanet research.”
Through the TESS Guest Investigator Program, the worldwide scientific community will be able to conduct research beyond TESS’s core mission in areas ranging from exoplanet characterization to stellar astrophysics, distant galaxies and solar system science.
TESS is a NASA Astrophysics Explorer mission led and operated by MIT and managed by Goddard. George Ricker, of MIT’s Kavli Institute for Astrophysics and Space Research, serves as principal investigator for the mission. TESS’s four wide-field cameras were developed by MIT’s Lincoln Laboratory. Additional partners include Orbital ATK, NASA’s Ames Research Center, the Harvard-Smithsonian Center for Astrophysics, and the Space Telescope Science Institute. More than a dozen universities, research institutes and observatories worldwide are participants in the mission.
An artist’s impression of an active red dwarf star irradiating an orbiting planet. Image credit: NASA/ESA/G. Bacon (STScI).
Low-mass stars are currently the most promising targets when searching for potentially habitable planets, but new research has revealed that some of these stars produce significant amounts of ultraviolet (UV) radiation throughout their lifetimes. Such radiation could hinder the development of life on any orbiting planets.
M-dwarfs are stars that are cooler and less massive than stars like our Sun, and are the most common type of star in the Galaxy, meaning that it is vital that we better understand them and the influence they have on their planets.
Detecting terrestrial planets in the habitable zone – the region where liquid water can exist on a planet’s surface – when they pass in front of, or transit, Sun-like stars is difficult. This is partly because we only see a small dip in the light as the planet crosses the star, and also partly because their orbits are long enough that we have to wait several years to observe multiple transits. However, because M-dwarfs are smaller and cooler, the planets in their habitable zone are much closer to their star, resulting in larger and more frequent drops in light, making them easier to detect.
This makes M-dwarfs ideal candidates when searching for potentially habitable planets, which has led to habitable zone terrestrial planets being discovered around M-dwarfs including Proxima Centauri, TRAPPIST-1and Ross 128.
Ultraviolet levels over time
A paper by astrophysicists Adam Schneider and Evgenya Shkolnik from Arizona State University, recently published in The Astronomical Journal,has revealed that the hottest and most massive M-dwarfs, referred to as ‘early type’, emit different amounts of UV radiation over their lifetime compared to the less massive and cooler ‘mid-’ and ‘late-type’ M-dwarfs. The paper used observations from NASA’s Galaxy Evolution Explorer (GALEX) spacecraft to study several populations of M-dwarfs in ultraviolet light.
M-dwarfs are known to emit higher levels of potentially harmful UV radiation than stars like our Sun. UV radiation can erode planetary atmospheres and have a detrimental effect on biology. It can also affect the abundances of molecules in planetary atmospheres, including carbon dioxide, oxygen and ozone. Ultraviolet light can break down molecules of carbon dioxide into their atomic components, producing atomic oxygen that then combines with molecular oxygen to form ozone. Ozone is easier to detect than oxygen, and is often thought to be a potential biomarker for life, so excessive UV radiation resulting in extra ozone could produce false positives where we mistake the extra ozone as a biological product. Therefore, understanding the levels of UV radiation emitted by M-dwarfs is essential for assessing the observations of their atmospheres.
Even though a planet orbiting a red dwarf might be in the habitable zone, allowing liquid water to exist on its surface, ultraviolet radiation from the star could affect the chemistry of the planet’s atmosphere. Image credit: M. Weiss/CfA.
The aim of the ‘Habitable Zones and M-dwarf Activity across Time” (HAZMAT) program is to use UV observations to understand how the habitability of low-mass stars changes over time. The researchers used GALEX to observe a large sample of M-dwarfs with known ages between ten million years and five billion years old.
Their results revealed that the lower-mass mid- and late-type stars retain high levels of UV activity with only a very gradual decrease over time, compared to the early-type M-dwarfs where the levels of UV radiation drop off quicker as the stars age.
The levels of UV radiation are very different across the early-type M-dwarfs, but this is not seen in the late-type stars. This could be due to the influence of stellar rotation. The lowest mass stars are fully convective, which means that the stellar material rises and falls in convective currents throughout the whole star. Higher mass stars are split into different zones, with a radiative zone as well as a convective zone where the energy spreads through radiation. Stars begin their lives rotating rapidly and then spin down over time as they lose momentum through the stellar wind. The stellar wind does not function efficiently in fully convective stars, so it is expected that the late-type stars would stay rotating rapidly for much longer than the early-type stars. Rotation is directly related to activity, so this could explain why lower mass stars are active for longer.
Harmful to life
The results suggest that lower-mass M-dwarfs have persistent UV radiation, which could rule out the possibility of life on any orbiting planets, including those around TRAPPIST-1 and Proxima Centauri.
“If the amount of stellar UV flux incident on a planet is harmful for life on that planet, then early-M dwarfs may be more desirable places to look for real estate,” says Schneider. “But, it is very likely not that simple. At first look, it may seem that our work suggests that stars such as TRAPPIST-1 and Proxima Centauri may be less likely to have habitable planets because of the prolonged UV activity of the lowest mass stars, but the notion of habitability is extremely complicated and there are many other factors besides UV flux that must be considered.”
Recent research by a team at Harvard University led by Sukrit Ranjan even suggests that planets around low-mass stars might not get enough of the right type of UV radiation needed for prebiotic chemistry to take place. “I think it’s still too early to say for certain whether or not prolonged UV activity is ‘good’ or ‘bad’ for a late-type M dwarf,” adds Schneider
The work was supported through NASA’s Habitable Worlds Program. NASA Astrobiology provides resources for Habitable Worlds and other Research and Analysis programs within the NASA Science Mission Directorate (SMD) that solicit proposals relevant to astrobiology research.
This composite image compares how big the moons of Mars appear, as seen from the surface of the Red Planet, in relation to the size that our Moon appears from Earth’s surface. While Earth’s Moon is 100 times bigger than the larger Martian moon Phobos, the Martian moons orbit much closer to their planet, making them appear relatively larger in the sky. Deimos, at far left, and Phobos, beside it, are shown together as photographed by NASA’s Mars rover Curiosity on Aug. 1, 2013. Image Courtesy of NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ.
Southwest Research Institute scientists posit a violent birth of the tiny Martian moons Phobos and Deimos, but on a much smaller scale than the giant impact thought to have resulted in the Earth-Moon system. Their work shows that an impact between proto-Mars and a dwarf-planet-sized object likely produced the two moons, as detailed in a paper published today in Science Advances.
The origin of the Red Planet’s small moons has been debated for decades. The question is whether the bodies were asteroids captured intact by Mars gravity or whether the tiny satellites formed from an equatorial disk of debris, as is most consistent with their nearly circular and co-planar orbits. The production of a disk by an impact with Mars seemed promising, but prior models of this process were limited by low numerical resolution and overly simplified modeling techniques.
“Ours is the first self-consistent model to identify the type of impact needed to lead to the formation of Mars’ two small moons,” said lead author Dr. Robin Canup, an associate vice president in the SwRI Space Science and Engineering Division. Canup is one of the leading scientists using large-scale hydrodynamical simulations to model planet-scale collisions, including the prevailing Earth-Moon formation model.
“A key result of the new work is the size of the impactor; we find that a large impactor — similar in size to the largest asteroids Vesta and Ceres — is needed, rather than a giant impactor,” Canup said. “The model also predicts that the two moons are derived primarily from material originating in Mars, so their bulk compositions should be similar to that of Mars for most elements. However, heating of the ejecta and the low escape velocity from Mars suggests that water vapor would have been lost, implying that the moons will be dry if they formed by impact.”
SwRI scientists modeled a Ceres-sized object crashing into Mars at an oblique angle. These four frames from the 3-D simulation show that the impact initially produces a disk of orbiting debris primarily derived from Mars (bottom right frame). The outer portions of the disk later accumulate into Mars’ small moons, Phobos and Deimos. The inner portions of the disk accumulate into larger moons that eventually spiral inward and are assimilated into Mars. Images/videos may be used by the media and the public for educational and informational purposes only
The new Mars model invokes a much smaller impactor than considered previously. Our Moon may have formed when a Mars-sized object crashed into the nascent Earth 4.5 billion years ago, and the resulting debris coalesced into the Earth-Moon system. The Earth’s diameter is about 8,000 miles, while Mars’ diameter is just over 4,200 miles. The Moon is just over 2,100 miles in diameter, about one-fourth the size of Earth.
While they formed in the same timeframe, Deimos and Phobos are very small, with diameters of only 7.5 miles and 14 miles respectively, and orbit very close to Mars. The proposed Phobos-Deimos forming impactor would be between the size of the asteroid Vesta, which has a diameter of 326 miles, and the dwarf planet Ceres, which is 587 miles wide.
“We used state-of-the-art models to show that a Vesta-to-Ceres-sized impactor can produce a disk consistent with the formation of Mars’ small moons,” said the paper’s second author, Dr. Julien Salmon, an SwRI research scientist. “The outer portions of the disk accumulate into Phobos and Deimos, while the inner portions of the disk accumulate into larger moons that eventually spiral inward and are assimilated into Mars. Larger impacts advocated in prior works produce massive disks and more massive inner moons that prevent the survival of tiny moons like Phobos and Deimos.”
These findings are important for the Japan Aerospace Exploration Agency (JAXA) Mars Moons eXploration (MMX) mission, which is planned to launch in 2024 and will include a NASA-provided instrument. The MMX spacecraft will visit the two Martian moons, land on the surface of Phobos and collect a surface sample to be returned to Earth in 2029.
“A primary objective of the MMX mission is to determine the origin of Mars’ moons, and having a model that predicts what the moons compositions would be if they formed by impact provides a key constraint for achieving that goal,” Canup said.
Perspective view of Ismenia Patera. ESA/DLR/FU Berlin
These images from ESA’s Mars Express show a crater named Ismenia Patera on the Red Planet. Its origin remains uncertain: did a meteorite smash into the surface or could it be the remnants of a supervolcano?
Ismenia Patera – patera meaning ‘flat bowl’ in Latin – sits in the Arabia Terra region on Mars. This a transition area between the planet’s northern and southern regions – an especially intriguing part of the surface.
Mars’ topography is clearly split into two parts: the northern lowlands and the southern highlands, the latter sitting up to a few kilometres higher. This divide is a key topic of interest for scientists studying the Red Planet. Ideas for how this dramatic split formed suggest either a massive single impact, multiple impacts or ancient plate tectonics as seen on Earth, but its origin remains unclear.
Ismenia Patera is some 75 km across. Its centre is surrounded by a ring of hills, blocks and lumps of rock thought to have been ejected and flung into the crater by nearby impacts.
The material thrown off from these events also created small dips and depressions that can be seen within Ismenia Patera itself. Gullies and channels snake down from the crater rim to the floor, which is covered by flat, icy deposits that show signs of flow and movement – these are likely akin to rocky, ice-rich glaciers, which have built up over time in the cold and arid climate.
These images were taken on 1 January by the high-resolution stereo camera on Mars Express, which has been circling the planet since 2003.
Such high-resolution and detailed images shed light on numerous aspects of Mars – for example, how the features seen scarring the surface formed in the first place, and how they have evolved in the many millions of years since. This is a key question for Ismenia Patera: how did this depression form?
Mars Express view of Ismenia Patera. ESA/DLR/FU Berlin
There are two leading ideas for its formation. One links it to a potential meteorite that collided with Mars. Sedimentary deposits and ice then flowed in to fill the crater until it collapsed to form the fissured, uneven landscape seen today.
The second idea suggests that, rather than a crater, Ismenia Patera was once home to a volcano that erupted catastrophically, throwing huge quantities of magma out into its surroundings and collapsing as a result.
Volcanoes that lose such huge amounts of material in a single eruption are termed supervolcanoes. Scientists remain undecided on whether or not these existed on Mars, but the planet is known to host numerous massive and imposing volcanic structures, including the famous Olympus Mons – the largest volcano ever discovered in the Solar System.
Arabia Terra also shows signs of being the location of an ancient and long-inactive volcanic province. In fact, another supervolcano candidate, Siloe Patera, also lies in Arabia Terra (seen in the context view of Ismenia Patera).
Certain properties of the surface features seen in Arabia Terra suggest a volcanic origin: for example, their irregular shapes, low topographic relief, their relatively uplifted rims and apparent lack of ejected material that would usually be present around an impact crater.
However, some of these features and irregular shapes could also be present in impact craters that have simply evolved and interacted with their environment in particular ways over time.
More data on the interior and subsurface of Mars will further our understanding and shed light on structures such as Ismenia Patera, revealing more about the planet’s complex and fascinating history.
In recent history, a very important achievement was the discovery, in 1995, of 51 Pegasi b, the first extrasolar planet ever found around a normal star other than the Sun.
Mayor and Queloz in front of the dome of the EULER 1.2 m-telescope at La Silla Observatory. Credit: Springer
In a paper published in EPJ H, Davide Cenadelli from the Aosta Valley Astronomical Observatory (Italy) interviews Michel Mayor from Geneva Observatory (Switzerland) about his personal recollections of discovering this exoplanet. They discuss how the development of better telescopes made the discovery possible. They also delve into how this discovery contributed to shaping a new community of scholars pursuing this new field of research. In closing, they reflect upon the cultural importance that the 51 Pegasi b discovery had in terms of changing our view of the cosmos.
Michel Mayor was born in Lausanne in 1942. He turned to astronomy when he did his PhD at the Geneva Observatory, where he focused on elucidating the theoretical nature of the spiral arms of galaxies, which make it possible for stars and nebulae to pass through without permanently remaining inside the arms. Later on his interest shifted to solar-type stars, and in 1991 he published the result of 15 years of work on the statistics of such solar-type stars. In hindsight, this paper played a significant role in boosting, at a later time, his interest in brown dwarfs and planets. He feels that the search for exoplanets was a direct continuation of that work.
He then relates what drove the development of a spectrograph called ELODIE, designed to offer very high sensitivity in measuring the radial velocities of stars. ELODIE commenced operation in April 1994, and Mayor and his colleague Queloz discovered 51 Peg b in July 1995. As the first planet ever discovered around a normal star other than the Sun, it was a ground-breaking achievement. A few years later, Mayor contributed to designing and building another state-of-the-art spectrograph, called HARPS, that is now allowing astronomers to probe the universe further. Altogether about 300 new exoplanets have been discovered by Mayor and his co-workers since 51 Peg b.
The Milky Way, our own galaxy, stretches across the sky above the La Silla telescope in Chile. Hidden inside our own galaxy are trillions of planets, most waiting to be found. Credits: ESO/S. Brunier
Step outside on a clear night, and you can be sure of something our ancestors could only imagine: Every star you see likely plays host to at least one planet.
The worlds orbiting other stars are called “exoplanets,” and they come in a wide variety of sizes, from gas giants larger than Jupiter to small, rocky planets about as big around as Earth or Mars. They can be hot enough to boil metal or locked in deep freeze. They can orbit their stars so tightly that a “year” lasts only a few days; they can orbit two suns at once. Some exoplanets are sunless rogues, wandering through the galaxy in permanent darkness.
That galaxy, the Milky Way, is the thick stream of stars that cuts across the sky on the darkest, clearest nights. Its spiraling expanse probably contains about 400 billion stars, our Sun among them. And if each of those stars has not just one planet, but, like ours, a whole system of them, then the number of planets in the galaxy is truly astronomical: We’re already heading into the trillions.
This rocky super-Earth is an illustration of the type of planets future telescopes, like TESS and James Webb, hope to find outside our solar system. Credits: ESO/M. Kornmesser
We humans have been speculating about such possibilities for thousands of years, but ours is the first generation to know, with certainty, that exoplanets are really out there. In fact, way out there. Our nearest neighboring star, Proxima Centauri, was recently found to possess at least one planet – probably a rocky one. It’s 4.5 light-years away – more than 25 trillion miles (40 trillion kilometers). The bulk of exoplanets found so far are hundreds or thousands of light-years away.
The bad news: As yet we have no way to reach them, and won’t be leaving footprints on them anytime soon. The good news: We can look in on them, take their temperatures, taste their atmospheres and, perhaps one day soon, detect signs of life that might be hidden in pixels of light captured from these dim, distant worlds.
The first exoplanet to burst upon the world stage was 51 Pegasi b, a “hot Jupiter” 50 light-years away that is locked in a four-day orbit around its star. The watershed year was 1995. All of a sudden, exoplanets were a thing.
But a few hints had already emerged. A planet now known as Tadmor was detected in 1988, though the discovery was withdrawn in 1992. Ten years later, more and better data showed definitively that it was really there after all.
And a system of three “pulsar planets” also had been detected, beginning in 1992. These planets orbit a pulsar some 2,300 light-years away. Pulsars are the high-density, rapidly spinning corpses of dead stars, raking any planets in orbit around them with searing lances of radiation.
Now we live in a universe of exoplanets. The count of confirmed planets is 3,700, and rising. That’s from only a small sampling of the galaxy as a whole. The count could rise to the tens of thousands within a decade, as we increase the number, and observing power, of robotic telescopes lofted into space.
This evocative movie of four planets more massive than Jupiter orbiting the young star HR 8799 is a composite of sorts, including images taken over seven years at the W.M. Keck observatory in Hawaii. Credits: Jason Wang/Christian Marois
How did we get here?
We’re standing on a precipice of scientific history. The era of early exploration, and the first confirmed exoplanet detections, is giving way to the next phase: sharper and more sophisticated telescopes, in space and on the ground. They will go broad but also drill down. Some will be tasked with taking an ever more precise population census of these far-off worlds, nailing down their many sizes and types. Others will make a closer inspection of individual planets, their atmospheres, and their potential to harbor some form of life.
Direct imaging of exoplanets – that is, actual pictures – will play an increasingly larger role, though we’ve arrived at our present state of knowledge mostly through indirect means. The two main methods rely on wobbles and shadows. The “wobble” method, called radial velocity, watches for the telltale jitters of stars as they are pulled back and forth by the gravitational tugs of an orbiting planet. The size of the wobble reveals the “weight,” or mass, of the planet.
This method produced the very first confirmed exoplanet detections, including 51 Peg in 1995, discovered by astronomers Michel Mayor and Didier Queloz. Ground telescopes using the radial velocity method have discovered nearly 700 planets so far.
But the vast majority of exoplanets have been found by searching for shadows: the incredibly tiny dip in the light from a star when a planet crosses its face. Astronomers call this crossing a “transit.”
The size of the dip in starlight reveals how big around the transiting planet is. Unsurprisingly, this search for planetary shadows is known as the transit method.
NASA’s Kepler space telescope, launched in 2009, has found nearly 2,700 confirmed exoplanets this way. Now in its “K2” mission, Kepler is still discovering new planets, though its fuel is expected to run out soon.
Each method has its pluses and minuses. Wobble detections provide the mass of the planet, but give no information about the planet’s girth, or diameter. Transit detections reveal the diameter but not the mass.
But when multiple methods are used together, we can learn the vital statistics of whole planetary systems – without ever directly imaging the planets themselves. The best example so far is the TRAPPIST-1 system about 40 light-years away, where seven roughly Earth-sized planets orbit a small, red star.
The TRAPPIST-1 planets have been examined with ground and space telescopes. The space-based studies revealed not only their diameters, but the subtle gravitational influence these seven closely packed planets have upon each other; from this, scientists determined each planet’s mass.
So now we know their masses and their diameters. We also know how much of the energy radiated by their star strikes these planets’ surfaces, allowing scientists to estimate their temperatures. We can even make reasonable estimates of the light level, and guess at the color of the sky, if you were standing on one of them. And while much remains unknown about these seven worlds, including whether they possess atmospheres or oceans, ice sheets or glaciers, it’s become the best-known solar system apart from our own.
An illustration of the different missions and observatories in NASA’s exoplanet program, both present and future. Credits: NASA
Where are we going?
The next generation of space telescopes is upon us. First up is the launch of TESS, the Transiting Exoplanet Survey Satellite. This extraordinary instrument will take a nearly full-sky survey of the closer, brighter stars to look for transiting planets. Kepler, the past master of transits, will be passing the torch of discovery to TESS.
TESS, in turn, will reveal the best candidates for a closer look with the James Webb Space Telescope, currently schedule to launch in 2020. The Webb telescope, deploying a giant, segmented, light-collecting mirror that will ride on a shingle-like platform, is designed to capture light directly from the planets themselves. The light then can be split into a multi-colored spectrum, a kind of bar code showing which gases are present in the planet’s atmosphere. Webb’s targets might include “super Earths,” or planets larger than Earth but smaller than Neptune – some that could be rocky planets like super-sized versions of our own.
Little is known about these big planets, including whether some might be suitable for life. If we’re very lucky, perhaps one of them will show signs of oxygen, carbon dioxide and methane in its atmosphere. Such a mix of gases would remind us strongly of our own atmosphere, possibly indicating the presence of life.
But hunting for Earth-like atmospheres on Earth-sized exoplanets will probably have to wait for a future generation of even more powerful space probes in the 2020s or 2030s.
Thanks to the Kepler telescope’s statistical survey, we know the stars above are rich with planetary companions. And as we stare up at the night sky, we can be sure not only of a vast multitude of exoplanet neighbors, but of something else: The adventure is just beginning.
The Earth’s tides weren’t always as energetic as they are today. A new study suggests that when tectonic movement molds ocean basins into certain shapes, the tides grow much stronger. And when tectonic movement opens those same basins millions of years later, the tides weaken. Credit: Creative Commons CC0.
The cyclic strengthening and weakening of ocean tides over tens of millions of years is likely linked to another, longer cycle: the formation of Earth’s supercontinents every 400 to 600 million years, according a new study. The new findings have implications for the formation of our planet, its climate and the evolution of life on Earth, according to the study’s authors.
The new research suggests long-term changes in tidal energy, which control the strength of the ocean’s waves, are part of a super-tidal cycle dictated by the movement of tectonic plates.
When tectonic plates slide, sink and shift the Earth’s continents to form large landmasses, or supercontinents, ocean basins open and close in tandem. As these basins change shape, they can strike forms that amplify and intensify their tides.
In the new study, tidal simulations projected hundreds of millions of years into the future suggest the Earth is now in the nascent stage of a tidal energy maximum, where strong tides will persist for roughly 20 million years. The oceans will go through several tidal cycles as the next supercontintent forms over the next 250 million years. Eventually, the tides will grow much weaker, just as they did during the two most recent supercontinents: Pangaea and Rodinia, according to the new study published in Geophysical Research Letters, a journal of the American Geophysical Union.
Scientists were aware tidal energy varied in the distant past, but the new study suggests there is a super-tidal cycle occurring over geologic timescales and linked to tectonic movement.
“Our simulations suggest that the tides are, at the moment, abnormally large,” said oceanographer Mattias Green from Bangor University’s School of Ocean Sciences in Menai Bridge in the United Kingdom and lead author of the new study. “And that really was our motivating question: If the tides were weak up until 200 million years ago, and they’ve since shot up and become very energetic over the past two million years, what will happen if we move millions of years into the future?”
Tidal strength is linked to life on Earth and understanding the ocean’s cyclic progression stands to inform scientists’ understanding of evolutionary history, according to the study’s authors. In times of strong tidal energy, like today, strong waves stir the sea, creating the nutrient mixing needed to sustain ocean life. As Earth’s landmasses move slowly toward a supercontinent configuration, the planet’s ocean basins open, eventually forming one unbroken mass of water. Such a sea would have low tidal energy. Weak waves mean there is less nutrient mixing, which could create an oxygen-starved ocean floor largely devoid of life, much like a pool of stagnant water, according to the new study.
The existence of this cycle and its link to tectonic movement stands to inform many disciplines, from evolutionary biology to global nutrient cycling, according to geophysicist Dietmar Müller from the University of Sydney in Australia, who wasn’t involved in the new study.
“It probably doesn’t mean anything to humans now in our lifetime,” Muller said. “But it does enhance our understanding of interactions between plate tectonics, Earth’s climate system, its oceans, and even how the evolution of life is, at least to some extent, driven by this tidal process.”
Changing continents, ocean basins
Each of Earth’s continents ride atop huge slabs of rock known as tectonic plates. These plates shift over hundreds of millions of years, striking different continental configurations along the way.
Tectonic plates dictate the shape and arrangement of continents, but they also determine the shape of ocean basins. As the North American and Eurasian plates drift apart, the Atlantic Ocean between them widens, also changing its shape.
The change in shape of ocean basins causes a change in a property known as resonance. When a basin is resonant, energy from the gravitational attraction of the moon aligns with the length of the ocean basin, causing an amplification of tidal energy.
Green likens resonance to a child on a swing set. A swinging child only needs a small push from an adult, at the right timing, to keep the swing moving higher and higher. “You force it at the same frequency as the natural oscillation, and the same thing happens in the ocean,” he said.
A tectonic timeline
In the new study, scientists simulated the movement of Earth’s tectonic plates and changes in the resonance of ocean basins over millions of years.
The new research suggests the Atlantic Ocean is currently resonant, causing the ocean’s tides to approach maximum energy levels. Over the next 50 million years, tides in the North Atlantic and Pacific oceans will come closer to resonance and grow stronger. In that time, Asia will split, creating a new ocean basin, according to the study.
In 100 million years, the Indian Ocean, Pacific Ocean and a newly formed Pan-Asian Ocean will see higher resonance and stronger tides as well. Australia will move north to join the lower half of Asia, as all the continents slowly begin to coalesce into a single landmass in the northern hemisphere, according to the new study.
After 150 million years, tidal energy begins to decline as Earth’s landmasses form the next supercontinent and resonance declines. In 250 million years, the new supercontinent will have formed, bringing in an age of low resonance, leading to low tidal energy and a largely quiet sea, according to the new research.
The new study finds each tidal maximum lasts at most 50 million years and is not necessarily in phase with the supercontinent cycle.
New images from the SPHERE instrument on ESO’s Very Large Telescope are revealing the dusty discs surrounding nearby young stars in greater detail than previously achieved. They show a bizarre variety of shapes, sizes and structures, including the likely effects of planets still in the process of forming. Credit: ESO/H. Avenhaus et al./E. Sissa et al./DARTT-S and SHINE collaborations
The SPHERE instrument on ESO’s Very Large Telescope (VLT) in Chile allows astronomers to suppress the brilliant light of nearby stars in order to obtain a better view of the regions surrounding them. This collection of new SPHERE images is just a sample of the wide variety of dusty discs being found around young stars.
These discs are wildly different in size and shape — some contain bright rings, some dark rings, and some even resemble hamburgers. They also differ dramatically in appearance depending on their orientation in the sky — from circular face-on discs to narrow discs seen almost edge-on.
SPHERE’s primary task is to discover and study giant exoplanets orbiting nearby stars using direct imaging . But the instrument is also one of the best tools in existence to obtain images of the discs around young stars — regions where planets may be forming. Studying such discs is critical to investigating the link between disc properties and the formation and presence of planets.
Many of the young stars shown here come from a new study of T Tauri stars, a class of stars that are very young (less than 10 million years old) and vary in brightness. The discs around these stars contain gas, dust, and planetesimals — the building blocks of planets and the progenitors of planetary systems.
These images also show what our own Solar System may have looked like in the early stages of its formation, more than four billion years ago.
Most of the images presented were obtained as part of the DARTTS-S (Discs ARound T Tauri Stars with SPHERE) survey. The distances of the targets ranged from 230 to 550 light-years away from Earth. For comparison, the Milky Way is roughly 100 000 light-years across, so these stars are, relatively speaking, very close to Earth. But even at this distance, it is very challenging to obtain good images of the faint reflected light from discs, since they are outshone by the dazzling light of their parent stars.
Another new SPHERE observation is the discovery of an edge-on disc around the star GSC 07396-00759, found by the SHINE (SpHere INfrared survey for Exoplanets) survey. This red star is a member of a multiple star system also included in the DARTTS-S sample but, oddly, this new disc appears to be more evolved than the gas-rich disc around the T Tauri star in the same system, although they are the same age. This puzzling difference in the evolutionary timescales of discs around two stars of the same age is another reason why astronomers are keen to find out more about discs and their characteristics.
Astronomers have used SPHERE to obtain many other impressive images , as well as for other studies including the interaction of a planet with a disc , the orbital motions within a system, and the time evolution of a disc.
The new results from SPHERE, along with data from other telescopes such as ALMA, are revolutionising astronomers’ understanding of the environments around young stars and the complex mechanisms of planetary formation.
An artist’s impression of the TESS spacecraft, which will discover exoplanets by watching them transit in front of their stars. Image credit: MIT.
The search for exoplanets is about to receive a huge boost, thanks to a new NASA mission called TESS – the Transiting Exoplanet Survey Satellite– that is set to embark on a quest to discover thousands of new worlds orbiting the brightest and nearest stars to the Sun.
“The number of Earth-sized and super-earth planets that TESS should find over the course of its two-year primary mission will be in the range of 500 to 1,000 new planets, and overall the number of planets that will be established is likely to be in excess of 20,000 all together,” enthuses MIT’sGeorge Ricker, who is TESS’ Principal Investigator.
TESS is the successor to NASA’s Kepler mission and is scheduled to blast off this week (its launch window opens on 16 April) from the Kennedy Space Center atop a SpaceX Falcon 9 rocket. The spacecraft will spend a minimum of two years patiently searching 200,000 stars all across the sky for the telltale dips in light that tell astronomers that there are planets transiting those stars.
Adding to the exoplanet catalog
Exoplanet hunting has been big business for the scientific community ever since the first worlds orbiting Sun-like stars were discovered in 1995. So far, over 3,750 exoplanets have been discovered. Many of these worlds are large and hot, or rocky and hot, although some are cool enough to potentially be habitable. Although the expectation is that TESS will identify up to 17,000 hot gas giants, up to 500 worlds among its treasure trove of discoveries are predicted to be rocky worlds, including about fifty that will be Earth-sized. Many of these will be in the habitable zones of their stars, where temperatures are just right for liquid water to exist on the surface of Earth-like planets.
The Kepler Space Telescope, which is running out of fueland will end its mission later this year, has discovered 2,649 planets and identified a further 2,724 candidate planets since it launched in 2009. Kepler discovered these planets by detecting what astronomers call ‘transits’.
A transit occurs when a planet orbiting its star appears to move in front of that star from our perspective. As it does so, it temporarily blocks a small fraction of the star’s light, resulting in a tiny change in the star’s brightness. A giant Jupiter-sized planet might block one percent of a star’s light, while an Earth-sized planet may obscure just 0.01 percent. These are tiny variations in a star’s brightness, but not beyond the reach of modern day digital sensors.
The problem is, at no time do astronomers ever directly see a planet that is transiting. We cannot resolve a planet’s silhouette against its star, even with our biggest telescopes. Since other phenomena, such as a plague of star-spots, or a close binary system of two orbiting stars, can also cause a star’s light to appear to dip, how do astronomers know that they have really detected a transiting planet?
Confirming that an exoplanet is real typically relies on measuring the planet’s mass, using a technique known as ‘radial velocity’. This is essentially just a fancy way of saying the Doppler shift. Just as sound waves from a passing police car rise and fall in pitch, so too do light waves from objects moving towards or away from us.
Although planets are much smaller than the star they orbit, their gravity still tugs on their parent star. This results in the center of mass between the star and planet being slightly offset from the centre of the star. Technically the planet orbits this center of mass rather than the star per se, and so does the star. So from our perspective the star appears to move, or wobble, around this center of mass, a motion that creates a slight Doppler shift in the star’s light. The radial velocity technique measures the speed of this wobbling motion. The more massive the orbiting planet, the stronger its gravitational pull and the higher the radial velocity. The confirmation of the wobble and the measurement of the mass of the orbiting body is sufficient evidence to indicate that a planet is present.
The TESS spacecraft in NASA’s Payload Hazardous Servicing Facility at Kennedy Space Center. Image credit: Orbital ATK.
Why do we need TESS?
The reason Kepler has found so many unconfirmed ‘candidate’ planets is because many of the stars that it has observed are just too far away and too faint for our telescopes to be able to measure the radial velocity accurately.
This is where TESS comes in. Following in Kepler’s footsteps by detecting exoplanets through transits, TESS will have the advantage of observing stars that will be, on average, ten times closer than the stars Kepler observed, at distances of a few hundred light years at most. Therefore they will be much brighter, which will make follow up observations far easier, resulting in more confirmed planets.
Furthermore, by knowing the mass of a planet from radial velocity measurements and the radius of a planet based on how much starlight it blocked, it is a simple calculation to determine a planet’s density, which can tell astronomers whether that planet is rocky or gaseous in nature, or whether it has a small core and a thick atmosphere, or whether it has a large core covered in deep oceans.
Furthermore, bright stars make something called ‘transit spectroscopy’ easier. As a planet transits its star, the starlight passes through the planet’s atmosphere, where atmospheric molecules, for example ozone or carbon dioxide, absorb some of the starlight. This absorption creates a ‘fingerprint’ in the star’s spectrum – black absorption lines at wavelengths characteristic of the specific molecules that are absorbing the light. By identifying these absorption lines, astronomers can determine what gases are in an exoplanet’s atmosphere. The brighter the star is, the stronger the absorption signal is and the easier it is to detect.
Transit spectroscopy is commonly done for large gas giant planets close to their stars, but currently only NASA’s James Webb Space Telescope, when it finally launches, has the resolving power to properly characterize the atmospheres of smaller, rocky worlds. It certainly helps if astronomers can find exoplanets that transit quite frequently, providing multiple opportunities to take measurements in a short space of time. This is why TESS is needed: it will find a multitude of interesting planets that other telescopes can follow up on and study in-depth.
Potentially habitable exoplanets orbiting red M-dwarf stars will be a key target for TESS. Image credit: David A Aguilar/Harvard–Smithsonian Center for Astrophysics.
Red dwarf regime
As it happens, there are star systems where rocky planets – and potentially habitable ones at that – are close enough to their star to transit quite frequently. These star systems are the M-dwarfs, which are small, cool stars such as red dwarfs that emit most of their light towards the red and infrared region of the spectrum.
“TESS has been optimized to look in near-infrared light,” says Ricker. “This means that, for the first time, we will open up the regime of M-dwarfs, which comprise about 75 percent of the stars in the Milky Way Galaxy.
M-dwarfs, previously ignored by astronomers, have grown more attractive to exoplanet hunters in recent years. This turnaround has been caused, in part, by ground-based telescopes discovering habitable zone planets orbiting nearby M-dwarf stars such as Proxima Centauri, TRAPPIST-1and Ross 128. TESS will transform our understanding of planets around M-dwarfs by searching thousands of them.
Because M-dwarfs are so small, with around a tenth of the mass of the Sun, their planetary systems are also on a much smaller scale than our Solar System. Indeed, the orbits of TRAPPIST-1’s seven planets could fit inside the orbit of Mercury six times over. Furthermore, because M-dwarfs are so cool, their habitable zone is also much closer in.
“The habitable zone for M-dwarfs corresponds to an orbital period for a planet of the order 10 to 14 days,” says Ricker. “So TESS should find a fair number of planets that are in the habitable zone for that class of star.”
TESS will observe the sky in 24 x 96-degree segments, with 13 segments per hemisphere. The segments converge towards the poles, meaning regions near the poles get longer coverage than nearer the celestial equator, allowing planets with longer orbital periods to be discovered. The region of maximum coverage also coincides with the region of the sky that will be in continuous view of the James Webb Space Telescope, allowing it to more easily follow up on the most promising planets found. Image credit: MIT.
Besides M-dwarfs, TESS will also look at other stars across a range of masses up to and beyond the mass of the Sun. Many of these stars will be the stars visible to the naked eye in the night sky, with only the brightest stars in the sky – such as Sirius, Rigel and Vega – being missed out because they are too bright for TESS’ optics.
TESS, armed with a quartet of wide-field 16.8-megapixel CCD cameras, will initially perform a two-year mission. During its first year it will scour the southern celestial sky, and in the second year, the northern sky. This is already an advantage over Kepler, which spent its primary mission staring at a single small patch of sky instead.
The cameras on TESS afford it a 24 by 96 degree field of view, which will stretch from the celestial pole down to about six degrees above the ecliptic plane. TESS will spend 27 days staring at each 24 by 96 degree segment, taking quick snapshots every two minutes and longer full-frame exposures every 30 minutes, watching for the telltale periodic dips in light of a transit.
The wider picture
Following it’s initial two-year mission, there are “options for its continuation,” Ricker tells Astrobiology Magazine, including a search of the stars in the ecliptic plane, which TESS will miss out in its initial survey. “The reason that TESS [h is two years is that it’s part of NASA’s Explorer Program, for which all the missions have a baseline operating period of two years. Then there’s an option for continuing the mission for an additional three years, and then there will be opportunities for extensions at three-year intervals going forward.”
TESS has four 16.8 megapixel cameras which will combine to create a 24 x 96-degree field of view. Image credit: NASA Goddard Space Flight Center/CI Lab.
Indeed, Ricker expects the mission to run throughout the 2020s, at least to when the European Space Agency’s PLATO(PLAnetary Transits and Oscillations of stars) spacecraft, which is another exoplanet hunting mission, launches. Nor is PLATO the only mission that will be joining TESS. Later this year the European Space Agency will launch a smaller satellite, called CHEOPS(CHaracterizing ExOPlanet Satellite), which will measure the densities of already-known exoplanets with a view to better characterizing those worlds. Further in the future there is also Europe’sARIEL(Atmospheric Remote-sensing Exoplanet Large-survey) mission, which will launch in about 2028 to probe the atmospheres of exoplanets. When it launches, NASA’s James Webb Space Telescope will also be able to scrutinize the atmospheres of some of the closest exoplanets, while the large surveys conducted by NASA’s forthcoming WFIRST(Wide Field InfraRed Survey Telescope) and the ground-based LSST(Large Synoptic Survey Telescope) currently under construction in Chile, will also find many more exoplanets, complementing the work done by TESS and Kepler before it.
Each of these telescopes and space missions will help piece together a bigger picture that describes the range of exoplanets out there in the Universe, how many planetary systems are like the Solar System, how many are different, and how common planets like Earth are, which leads to the next great question: do those planets have life? Indeed, if TESS is successful then it may well find the first truly Earth-like planet around another star. That star is quite possibly going to be one that we can see in the sky with the unaided eye during a dark night. So the next time you go outside to look at the stars, take some time to wonder about what worlds might be out there, because in a few years time, thanks to TESS, we will hopefully know.
The Gravity Assist Podcast is hosted by NASA’s Director of Planetary Science, Jim Green, who each week talks to some of the greatest planetary scientists on the planet, giving a guided tour through the Solar System and beyond in the process. This week,he’s joined by Faith Vilas of the National Science Foundation to discuss Mercury and what we know about the innermost planet from NASA’s Mariner 10 and MESSENGER missions.
You can listen to the full podcast here, or read the abridged transcript below
Mercury, seen during MESSENGER’s first fly-y in 2008. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
Jim Green:Faith, you were researching Mercury well before the MESSENGER mission. How did you get involved in Mercury research?
Faith Vilas: Well, I was an undergraduate working with a professor over at MIT, and I wanted to do some independent study. He suggested I take a look at Mercury. Now, Mercury is not an easy object to observe from the Earth, either from the surface or even from something like the Hubble [Space Telescope], because it only goes, at most, 28 degrees away from the Sun. So, it’s sort of one of those projects that you take on, and you’re going to do it, and you’re standing on a ladder, and you’re tilting your telescope over near the horizon, and you can barely see it. You can follow it a little ways, but it’s always near the Sun, which you always have to watch out for. It becomes a tricky object to observe.
Jim Green:The scientific community made some predictions about Mercury before MESSENGERactually reached it. What were some of those things that proved to be correct?
Faith Vilas: The prediction that I made that proved to be correct, which I’m grateful for, was that there were no iron oxides; there’s no oxidized iron in the surface material of Mercury.This flies in the face of the fact that we know that Mercury is very heavy, it has a very large core of iron and nickel metal. Every prediction was that it was going to have plenty of oxidized iron on thesurface,and I said, no, I don’t see it. Then when we got there with MESSENGER, sure enough, [we found that] it’s not ther
The reason people thought I may be wrong is that because Mercury is so close to the Sun, it’s so hard to observe, we have to look through [more of Earth’s] really thick atmosphere down near the horizon. [The seeing conditions] vary very quickly. It could affect your spectra if you’re not being very careful about your observations.So, it needed MESSENGER to be able to solve that.
Jim Green:Was there any indication from ground-based telescopes that there could have been ice on Mercury?
Faith Vilas: Yes, there were, and they came from the radar at Arecibo in Puerto Rico. The observations were made near the poles of Mercury. The first indication was that it looked very different, and that it was maybe asignature of water-ice, but why would it be there [at Mercury’s poles]? Then they continued the observations and were able, with improvements in the radar, to narrow them down to specific areas at the north and south poles.
With the images we got from Mariner 10, it was possible to show that some of these signals matched where the craters were. So, we started thinking that what’s going on here is that we have craters at the poles that are in [permanent] shadow because Mercury doesn’t tilt very much on its axis, so the Sun never reaches them and they can keep water and ice there as long as they want to keep water and ice there. The question then became, where did the water come from? It largely looked like it came from sources outside of Mercury; because Mercury’s so close to the Sun, everything’s going to be focused into crashing into it, and water-ice comets came in and impacted, and trapped a whole bunch of the water-ice at the poles.
One model for how Mercury got its unusually high-metal content is a collision with another planetary body that stripped Mercury of its outer layers, leaving just its dense core and mantle. Image credit: NASA/JPL–Caltech.
Jim Green:What other surprises have we found on Mercury?
Faith Vilas: Everybody thought that Mercury was going be a bland and boring little planet. [People think that] Mercury looks like the Moon. It’s actually significantly different than the Moon. Things that were not predicted that we did see were [the presence of] lots of other materials. We had some really unusual features and bright features, features with what we assume is sulfur, which we have not yet fully explained.One of the things that was in question when we went to Mercury was whether there was [or had been] volcanism, and there sure was. The whole planet has had flowing volcanoes at different times. [There isn’t]the really super-high volcanoes, like the mountains we get on Mars and Earth, but there’s obviously [been] a lot of volcanic activity on Mercury. Mercury was a very active planet at some point.
Every planet is vastly different, they all have a much more interesting history than we ever imagined. So to predict that Mercury is going to be this way because it looks this way, well, what we know that is wrong because it’s always [going to be] different. I’ve been fortunate to live through seeing the first really good look at these planets, and I predict that there’s so much more we can still learn from them. That should give us a reason to go to these objects, because we’re learning new things. That is also extended to exoplanets now, too.
Jim Green:Mercury is a small terrestrial body, it’s smaller than Mars and one would expect that it’s probably one of the more populous exoplanet.
Faith Vilas: What’s really interesting is the [large] number of exoplanets that are closer to their host star than Mercury is to our Sun. We still, I believe, think that Mercury did not form in its current location and has since moved in towards the Sun.So, we have this scenario where we see these big planets, very hot Jupiter-sizedplanetsorbiting super close around their stars. Why are we seeing this, and does this also play back into the huge amount of diversity that we see in planetary systems, not only in our own Solar System but in other planetary systems? We’re learning so much about that now.
Radar imagery superimposed on a MESSENGER image of Mercury’s north pole, showing the presence of water-ice (in yellow) hidden in permanently shadowed craters. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
Jim Green:This may sound crazy, but since Mercury’s core is so large, comparable perhaps to the size of Earth’s core, it’s almost like perhaps Mercury was thecoreof a larger planet.
Faith Vilas: That’s a thought that’s been around for a long time. It’s certainly a good, viable thought. It looks like it could have been a core from a larger planet, that what we see in the way of the ‘crust’ around Mercury now is actually just the layer that was above the core when, for some reason, the planetary surface was stripped away from the rest of the planet, which might have happened in the very early Solar System when we expect there was a huge, violent migration of objects throughout the Solar System. Things didn’t just happily form in one place. They formed in other places, and then the Sun and Jupiter and Saturn got busy and kicked everything [around], and then planets hit other planets, things fragmented, asteroids hit things, and Mercury may well have hit another planet that formed elsewhere in the Solar System, and its core might have been kicked into Mercury’s current location.But I don’t think we fully have the answer yet.
Jim Green:The concept that there were impacts during planet migrations has led us to think about small bodies, and one set of small bodies that we’re quite interested in finding are called the Vulcans. What do we know currently about them.
Faith Vilas: That we haven’t found any yet. We have not found any Vulcans.
Jim Green:So, what are they?
Faith Vilas: Vulcans are asteroids that are proposed to be between Mercury and the Sun. So far, we’ve looked for them using all sorts of different and creative methods, and we have not found them, not with MESSENGER, not with ground-based work, not with space-based work. We’ve seen plenty of objects between Venus and Earth, and Earth and Mars, and then of course there is the very heavy concentration of asteroids between Mars and Jupiter. But, we do not see anything between Mercury and the Sun.We see comets come through and crash into the Sun, but we haven’t seen any asteroids in that area.
Mercury’s huge Caloris basin, which at 1,550 kilometers in diameter is one of the largest impact basins in the Solar System. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
Jim Green:We also have to think about our Solar System as a point in time.As you point out, there’s been quite a bit of evolution. So when we look at other planetary systems, they are at a different point in time in theirevolution. We are still in an evolving Solar System.
Faith Vilas: [The Solar System] is not a dead system by a long shot. My reaction to what you’re saying is sort of mixed, because a lot of the other systems that we see with exoplanets around other stars, many of them are solar-like stars, and ultimately we’re looking for life, let’s face it.We’re looking for the life that we know about, and so, in looking for life as we understand it, which is carbon-based, we look for the types of objects that [would support that]. Kepler looked at a group of solar-like stars. Our ground-based observations look at solar-like stars, as well as the cooler stars and sometimes I’m sure the hotter ones, as well. We see disks of dust around other stars, which is what we expected to see and is what we think our Solar System started out like.Now we’re beginning to see some disks that have gaps where planets have formed. It’s truly amazing what we’re seeing, [which is] all sorts of variations and different types of planets, we’re seeing planets at different moments in formation, things I never thought I would see in my lifetime.
Jim Green:You’ve led an exciting scientific life. What was the ‘gravity assist’ that got you interested in planetary science?
Faith Vilas: When I was in the second grade, somebody gave me a copy of a book called The Golden Book of Astronomy. At this point neither we nor the Soviet Union had any astronauts in space. But, I looked at this book and said, I want to work on this. I want to work on these planets. I want to work on these astronomical things. I want to work on galaxies. I wanted to be part of the space program. I wanted to be part of our exploration, I wanted to be part of humankind going into space and looking at these planets that I used to fantasize about studying. That’s really what got me started in this. From that point on, mixed in with some other things that I chose to pursue periodically as I was growing up, I always came back to wanting to be an astronomer, because I wanted to study these objects.So when I got to high school and then college, that’s what I did.But, my gravity assist was in the second grade. It was The Golden Book of Astronomy.