uranus and neptune are called ice giantsuranus and neptune are called ice giants

Uranus and Neptune are called ice giants because they are smaller and compositionally different from Jupiter and Saturn, the gas giants. Uranus and Neptune contain deep atmospheres of molecular hydrogen, vast internal oceans of water, methane, and ammonia ices that melted due to high temperatures. The presence of methane accounts for the deep blue appearance of this planet, earning it the nickname blue planet. Neptune is the densest of all the giant planets. "Two fast, simple, affordable (FSA) orbiters can be launched if one of those crafts is solar-powered," Horzempa explains. Millot/J.Wickboldt/LLNL/NIF, Hydrogen ions (pink) flow within a solid lattice of oxygen in superionic ice. But, we've actually in the last few years seen another Great Dark Spot. The interiors of Uranus and Neptune: current understanding and open Y2RmMjcxNmU3OWNhMWVmMzNjZTk5MjFkMTdiNTM2ZWJkN2FkZWFhMWVkNDQw Neptune is the only planet that we cannot see with the naked eye. MWEwNjM3MGQ1MzQ1YzllMTI2ZjU4YmZlOTNiYTg4NTRmYTg4MWU2NTk3NmFj This steady stream from the Sun did not strip off the gases of the gas giants because they are much farther from it. In May this year, astronomers announced that they had found 62 new moons orbiting one of the Solar System's gas giants, the ringed planet Saturn. But an international team of researchers recently came up with a new explanation. Jim Green: Our solar system is a wondrous place with a single star, our Sun, and everything that orbits around it - planets, moons, asteroids and comets - what do we know about this beautiful solar system we call home? Scientists categorize exoplanets based on the planets of our solar system. This site uses cookies to assist with navigation, analyse your use of our services, collect data for ads personalisation and provide content from third parties. Gas Giants: Facts about the 4 Outer (Jovian) Planets The area called the Great White Spot or the Great White Oval has been observed periodically. If you believe Wordfence should be allowing you access to this site, please let them know using the steps below so they can investigate why this is happening. Even if we can't see the clouds, we can see the change in their light curves. Both ice giants have hydrogen, helium, and methane in their atmospheres, although scientists think that hazes formed . YjBmOTg4YWU1YzVjMDMzOWE4YWUyODlkYzAzN2VkNTVjZDFkZWE3NDVhOWQz These four are also called the Galilean moons. According to the researchers, the visible and near-infrared spectra of the atmospheres of the ice giants have long fascinated scientists,MailOlinereported. But Earth isnt the only icy world we know of. Super Neptune Exoplanet Has Water Vapor In Its Atmosphere Providing Clues on the Gas Giants in the Solar System, Hazy Blue Worlds: A Holistic Aerosol Model for Uranus And Neptune, Including Dark Spots, Could It Be Raining Diamonds in Uranus and Neptune? In Depth | Neptune - NASA Solar System Exploration It's tilted over 98 degrees. Far-flung Uranus and Neptune -- the ice giants of our solar system -- are as mysterious as they are distant. A gas giant may be classified as a planet whose original composition is of gases, such as hydrogen and helium, with a small rocky core. No other spacecraft has ventured there since. And even to do our own mission to one of these planets, we want to know more before we get there. It's--they're hard to see because they are so narrow. Lets get to know the four of them. Thank you for taking time to provide your feedback to the editors. Soon after its launch in 2021, NASA's James Webb Space Telescope will . There's so much for us to learn. It's a gigantic anti-cyclone, so it's a high-pressure storm. Cloud bands and winds on Uranus are lined parallel to the planet's equator controlled by the planet's rapid spinning rather than the Sun's heat. And we think they move around a little bit, too, which is interesting. Check out more news and information on Uranusand Neptunein Science Times. The gas giants Jupiter and Saturn contain far more gas than rock or ice. Stewart, Suzy. Volume 57.74 Earths "Less ambitious missions will deliver less science, but they have a better chance of achieving a coveted new start.". With me today is Dr. Amy Simon. All of the outer planets have rings around them. Amy Simon: Yeah, that's another big puzzle. And even though they're cold, they still have some sort of activity that's moving the ice around. And we think that is slowing down convection inside the planet. View our Privacy Policy. Since it is a gas giant and is composed mostly of hydrogen, this planet does not have a solid surface. And the instrument I was working at was based at NASA Goddard. It was being considered alongside a similar mission to Neptune called Neptune Odyssey. Gas Giants. Although ice giants have already been classified separately, Uranus and Neptune are still commonly called gas giants alongside Jupiter and Saturn. NASA just rejected missions to Jupiter's and Neptune's moons. Ice Giants Atmospheric Anomalies Mission Possible References Distant and obscure, the giant planets Uranus and Neptune lurk in the dark far from the Sun. The ice giant terminology took hold in the 1990s when researchers realized Uranus and Neptune were compositionally different from Jupiter and Saturn. So, it's not directly in the center of the planet, and it's also not just a north and south. Most of the material in the nebula was pulled to form the Sun. "The ice giant Orbiters will build on the experience of previous such missions. Planet Saturn is 9.5826 AU from the Sun. They are named after characters from the literary works of authors William Shakespeare and Alexander Pope. The short videos take audiences behind the scenes to learn more about how space missions come together. Methane absorbs light at 600nm, which is at the red end of the color spectrum but reflects blue. But, the fact that we have rings at all around the outer planets tells us they're pretty common. OWMwZWQ2MWE3YzJlYzhmZmVjNzU4N2E2OGU3ZWU3MGU0NDE2MzljYWJlNTZi Amy Simon: So, at the moment, we're seeing a lot more clouds on Neptune, and we're finding that they vary on really short time scales, and that's partly because it has winds that blow hundreds of miles an hour. The science-fiction writer called all giant planets "gas giants.". Gas giants of this class are largely made up of ammonia clouds. So, it is pretty much rolling around on its side. Moore Boeck. And Uranus' are very narrow. Hi, I'm Jim Green, Director of Planetary Science at NASA, and this is Gravity Assist. Uranus is the source of more than a few jokes and witty (and not so witty) puns, but the ice giant and its moons has been a serious destination various fictional stories, and on TV shows such as "Doctor Who." The radioactive element uranium was named after Uranus when it was discovered in 1789, just eight years after the planet was discovered. Mass 17.147 Earths ODZhNmI5NTY3N2FhODc5MjUwY2MxYmQ3MjI4OGI5ZGVjZjc2ZDQwNmVjMmRl Unfortunately, the development of the next generation of RTGs was canceled. Amy Simon: Absolutely. Uranus orbits at 19 AU with a . In his white paper, Horzempa keeps coming back to the idea that flagship missions that try to accomplish too much at once are likely to be rejected. YTNlNzY3ZmQ1MGM2NzIyZmI5NWUxMTJlMGYzNWExYWNmZDFhMDViOGNlMjdm And they kept inferring there had to be something else out there or something with a lot of mass pulling them around. Both Jupiter and Saturn belong are class I gas giants in this scheme. And so, they really are quite different planets from each other. Neptune wasn't seen for almost 50 years later, in 1846. And we're talking about the ice giants. Click here to sign in with But, when we looked again with Hubble when we could first look at Neptune, it was gone. Jim Green: Uranus is one of those planets that I think is so featureless. They are designated using the Greek alphabet system. Please let us know if you find any discrepancies or inaccuracies. We're actually looking every year now with Hubble at both of these planets. Just like other planets, Saturn also has storms. The rest of the nebula that was not used in its formation swirled around the Sun forming an accretion disk. Jim Green: Well, I'm here with Amy Simon, planetary scientist from NASA Goddard, and we're talking about Uranus and Neptune, our ice giants. The largest of such objects are the eight planets, in order from the Sun: four terrestrial planets named Mercury, Venus, Earth and Mars, two gas giants named Jupiter and Saturn, and two ice giants named Uranus and Neptune. The terrestrial planets have a definite surface and are mostly made of rock and metal. Seeking answers, planetary scientists plot a return to the nearest ice The Moon will appear full from early Thursday morning through early Sunday morning. The giant planets are very far from the Sun. Possible class IV gas giants include HD 209458 b, TrES-2b, and 55 Cancri b. Besides being much more Earth-like in its tilt--Neptune's tilted about 28 degrees--it's not the same color as Uranus. OGQzMDU4NmM1NWVmM2M4MGRmMDUwYjBiMWRlMTRlM2Q2MmNlMmY2NjE5ODRl Europa is one of Jupiters many moons. But, for Neptune, there's that one big moon Triton, and then the rest are much smaller. The pair of ice giants are the furthest two major planets in our solar system, and they . YjE1ZjE1N2ZkYTQ5YzdhZTcwMDNlN2EzZjE1ZTMxYWE3NmFmNDUzM2RhN2E1 But, rings are great because they're one way that we actually can do kind of the equivalent of seismology on the planets. Still, that does not mean that these planets are similar. Of all the planets in the solar system, only Uranus and Neptune called the ice giants because they are composed mostly of ices remain relatively unexplored. In astrophysics and planetary science the term "ices" refers to volatile chemical compounds with freezing points above about 100 K, such as water, ammonia, or methane, with freezing points of 273 K (0C), 195 K (78C), and 91 K (182C), respectively (see Volatiles ). You can also search for this author in PubMed We've also been using the Kepler Astrophysical Telescope to look at the light curves and study how their clouds are changing. What are ice giants called? Solar System 'hiding secret world' called Planet X And we've never even seen the other side of Triton, so who knows what's on the other side? And has there ever been lightning found on Uranus and Neptune? The authors of the study said that future observations would help answer the remaining questions and hopefully, the James Webb Space Telescope could uncover these mysteries during the planned observations for both planets. Gravity Assist: Ice Giants (Uranus & Neptune) with Amy Simon One of the critical pieces for simple and affordable missions concerns the power source. [Learn more facts about Jupiter]. For one thing, we think it has geysers on it, but these aren't geysers like we're used to on Earth where we have hot water and steam. Several NASA spacecraft, such as the Lunar Reconnaissance Orbiter, have found evidence of water ice. Saturns moon Enceladus has a water-ice crust over a saltwater ocean. Inclination 1.770 (to the ecliptic) ZGI5MGIxNTRjYzZmNThlMzI0ZDZkNTU3ODY1NGM5MzUwNzlmZTU1NGJhZTJj Amy Simon: Yeah, it really is unique. N2NjNzg2MDA4NmRhZjA1ZTk5ODZkODE1OGJlZDBhNTM4MDk3NzIxNzhiYTE0 It had to go around the Sun at least once during that time period to be able to understand its full perturbations. But, Triton doesn't. Jim Green: That's kind of amazing when we think about that. Decoupling probe missions from orbiter missions is one way to develop missions that are fast and affordable. Known Moons 14. Saturns icy moon Enceladus as viewed from NASA's Cassini spacecraft.Credit: NASA. He says that NASA should set the cost, outline the objectives, and let the commercial sector tackle it. And on these cold planets, the water ice is way down deep. Finding Neptune: How we discovered the eighth planet. March 13 marks 240 years since William Herschel discovered Uranus, 40 years after Voyager, scientists push for new missions to Uranus and Neptune, Astronomy Magazine Collection 2016-2020 DVD-ROM. The Moon will appear full from early Thursday morning through early Sunday morning. NASA's Grand Tour program in the 1970s called for four probes: two would've visited Jupiter, Saturn, and Pluto. Jim Green: You know, are there any analogies between that cantaloupe terrain and some of the terrain we see on Pluto? It was called the enhanced-MMRTG and would've delivered more power than previous RTGs. But the "ices" in Uranus and Neptune are below a top atmo. It also has lakes and rivers just like the Earth. Gas giants are planets that are very different from our own. Amy Simon: They are. They all pretty much rotate in the same direction. Rovers are enormously complex, and sample-return missions ratchet the complexity up even further, though neither of those is explicitly relevant to the ice giants. And they didn't quite form as big as, say, Jupiter or Saturn. NjkwMmI4NDg1YzgyNWVhYTc4MGNiMWNlNDgyMjNhNzllOGZiZDRjNmM0MjJk And so, that's kind of part of why we believe they're so different. googletag.cmd.push(function() { googletag.display('div-gpt-ad-1449240174198-2'); }); But complex missions to Mars and the moon are eating up budgets and shoving other endeavors aside. Amy Simon: That's correct, actually. We do not sell, rent or trade our email lists. Gas giants have existed for billions of years and we have never seen the formation of one yet. And I think the primary thing we'd add to any mission is an atmospheric probe, because we want to understand what the layers are in the atmospherewhat the temperatures are. While flagship missions including probes are not the priority in ice giant missions, neither should probes be forgotten. Universe Today. The New Horizons mission and the Parker Solar Probe have similar backstories. Still, the universe remains a big mystery, but these theories can help us understand how things may have started. Why are Uranus and Neptune different colors? - EarthSky These arcs are called Libert (Liberty), Egalit (Equality), Fraternit (Fraternity), and Courage. Horzempa points out that there's a historical precedent for this. Amy Simon: I think poor Uranus is misunderstood, actually. Known Rings 5 Why are uranus and Neptune called the ice giant planets? So, when it passed its equinox, so kind of its springtime, suddenly, we saw an outbreak of clouds all over the place, and we haven't seen a whole lot since then. Also, the storm of the Great Red Spot has been going on for so many years. In Depth | Uranus - NASA Solar System Exploration An image of Jupiters moon Ganymede taken by NASAs Galileo spacecraft.Credit: NASA/JPL. ZDRiNWQzODRiYmMzYmE4OTc2NTdmM2RjODZkMWJhMTljNTE1ZGJkM2NlY2I0 For general inquiries, please use our contact form. https://solarsystem.nasa.gov/resources/681/solar-system-temperatures/ Jim Green: You know, I think it took a long time to really find Pluto because of Uranus' perturbations. By signing up you may also receive reader surveys and occasional special offers. These sunless planets just wander aimlessly in space! As the largest planetary member of the solar system, it has a fitting name. Institution: Jet Propulsion Laboratory We believe many important atmospheric science questions can only be addressed by studies of the ice giants Uranus and Neptune. How were they able to acquire that? Jim Green: You know, Triton's such a spectacular moon. Amy Simon: So, Uranus was first seen by Hershel in 1781. And we've learned this while look at the other planets, at Saturn especially, because it has such extensive rings. A bright cloud lies at the cap's edge and a second one is seen at left. "With a limited payload, first priority goes to imaging," Horzempa writes. Well, it turns out, when it passes behind the rings, the same thing happens. NDIwYjA3OTBjMjY2MGNmZTdlMjgwMDA1ZWZkZTgxYTFlMDE3NTYzMjczNGY3 Through gravity and more collisions, the eighth planets were formed. So, each of the seasons is 21 years. It's kind of a pale blue planet. This is why they are called gas giants: They are mostly gaseous, with very little rock and ice. Momentum is building among planetary scientists to send a major mission to Uranus or Neptune the most distant and least explored planets in the Solar System. MjgxNmM1YjY3Mjk1N2I4Zjc1NjExNzMwNmQ2YWNjOGJhMjUyNTdhZTNkZDY0 What would happen if all the ice melted on Uranus and Neptune? And so, that's a real puzzle when we try to explain how the solar system formed. It's the real pale blue dot. Jim Green: As a civil servant, you provide opportunities during the summer for students to come and work. Interestingly, there are way more of them outside the solar system. This makes the orbiters more simple and cheap, which increases the likelihood that they will be approved. It's been over 35 years since a spacecraft visited Uranus and Neptune. It is easy to see why Uranus and Neptune are sometimes called "twin planets". YTBiYjIzNmFhNTJmNGRlN2Q2MThlN2MxNjNjMTE3ZGQ1NjAyY2Y0MGI5YzE5 After the Moon and the hottest planet, Venus, Jupiter is the third brightest object we can see in the night sky. Other names we can call gas giants are giant planets or jovian planets. One of six instruments aboard the agencys Mars Reconnaissance Orbiter, CRISM produced global maps of minerals on the Red Planets surface. Why is that such a different moon? It is believed to have existed even before 1665. The Four Planets With Rings Might Surprise You | HowStuffWorks Neptune is the eighth planet from the Sun. But there are fascinating worlds further out in the solar system that are begging to be explored. Is There Ice on Other Planets? - NASA Space Place PDF Outer Planets: The Ice Giants - Lunar and Planetary Institute (LPI) Orbital Period 164.8 Earth years These planets are known as Jovian Planets. Both planets have the same atmosphere with similar tropospheric temperatures. Study lead author Patrick Irvin said that this layer is called the Aerosol-2, which looks whitish at visible wavelengths and acts to lighten Uranus, which explains why the seventh planet in the Solar system has a paler shade of blue compared to Neptune. However, it has a very long orbital period which takes roughly 165 years here on Earth. Subscribe via Apple Podcasts Amy Simon: Correct. "The initial mission would be a Saturn Probe. OWNjOGYxNTEyOGI0NDE5OGYzOWMyODAxNDMyN2MyNmEyZDhiNjgxN2VkYjJk Later this decade, there are two launch windows that can take advantage of Jupiter gravity-assist maneuvers. Five are major moons, 13 are inner moons, and 9 are irregular moons. It is nearly 11 hours on Saturn, and about 17 and 16 Earth hours on Uranus and Neptune respectively. "This paper does not put forward a specific design but, rather, asks the Decadal team to endorse a competitive approach to the exploration of the ice giant systems," Horzempa states in his conclusion. These rings are mostly made up of ice and rock. She's a planetary scientist from NASA's Goddard Space Flight Center. The Atmospheres of the Ice Giants, Uranus and Neptune We get a different view than we do when we fly by other planets. What did Voyager 2 discover about Neptune during its fly-by that really surprised us? It only occurs at temperatures matching those on the Sun, and pressures exceeding a million Earth atmospheres precisely the environment predicted , To continue reading, subscribe How did you become an employee for NASA? Instead of methane, carbon monoxide becomes the dominant carbon-carrying molecule in the atmosphere. Join us next time as we continue our virtual tour of the solar system. The two have comparable masses (14.5 and 17 . They are believed to exist at temperatures less than about 150 K (120 C; 190 F). As the farthest planetary member in our own solar system, it is roughly 30 AU away. Classification All spacecraft are high-tech endeavors, but orbiters themselves are the most well-understood design. So, those clouds change really fast. water or methane etc molecules which would really be frozen if they were e.g. It's made of a thick soup of water, ammonia, and methane over an Earth-sized solid center. The largest natural satellite of Neptune, Triton, is the only large moon with a retrograde orbit. And again like Uranus, its interior is primarily ices and rock. They played a role in the evolution of the solar system, they're similar to many exoplanets we find in distant solar systems, and our brief encounters with them gave us only tantalizing glimpses. It is famously known as the ringed planet because of its bright and magnificent rings. (Also, see NASA Pathways program: https://nasajobs.nasa.gov/studentopps/pathways.htm). Triton also has geysers. NmNlNmRhMDNjZmE4YjRmOTE2NzdmYjNjYjBlZWMxODNjZDJhZTI5MzE0M2Rj Naomi Rowe-Gurney, a researcher at NASA's Goddard Space Flight Center whose focus is the atmospheres of the ice giants, toldNew Scientistthat comparing the color of the two ice giants is rare. Generated by Wordfence at Wed, 5 Jul 2023 18:55:46 GMT.Your computer's time: document.write(new Date().toUTCString());. eyJtZXNzYWdlIjoiM2JiYjk0NzRkNWUxMWRlYTlkZGQxZDUxYWU5MDBmNDU4 Not only are they very different from their rocky relatives ( Mercury, Venus, Earth and Mars), but also from the gas giants. Especially the ice giants Uranus and Neptune. Amy Simon: Oh, absolutely. NASA has plans for a Next Generation RTG, but there are no firm dates attached to it and no guarantees it will be built. So, we see arcs --partial rings--at various points around the planet. Stewart, Suzy. YTdjYzNlZGM2MTNjYTE5N2FhMWFkYTBjMzRlMTNjMjhlYzI4ZGI4Yzk4MWMy Examining Ice Giants With NASA's Webb Telescope | NASA This Week in Astronomy with Dave Eicher, 2023 Astronomy Calendar & Observer's Handbook, Astronomers have a new theory for why Uranus spins on its side. It is mostly made up of ices and other hydrocarbons. It's retrograde. These planets are not completely gaseous though . These protoplanets orbited our Sun for about 10 to 100 million years. But, we also looked at orbiters, and these are nice because it gives you a chance to explore that whole system - the rings, the moons, Triton in particular - to see what's going on on all sides of those different moons. China Rocket Crash: How Did NASA, ESAs Space Chiefs React to Chinese Long March 5B Rockets Uncontrolled Reentry to Earth? NTdhYjFmNmJmMmE3YWJhMWI4YzdlOTg4ZDBkOWI2MDg0MTc5ZmFkMDAyYmY1 The words gas giants already tell us something about their size and composition. NASA Completes Study of Future 'Ice Giant' Mission Concepts ISSN 1476-4687 (online) Imagine what dedicated orbiters could discover with modern technology. A total solar eclipse will darken a swath of North America as the Moon blocks the light of the Sun for a few minutes on April 8, 2024. The Planets. However, we do not guarantee individual replies due to the high volume of messages. Amy Simon: So, we've studied quite a lot of different ways to get out to Uranus and Neptune. And the fact that we haven't seen the other side of any of these moons, we have no idea what's out there. Uranus and Neptune are commonly called ice giants because they have a greater percentage of heavy elements compared to the gas giants, Jupiter and Saturn. Probes could still come later, Horzempa says, which can be an advantage for future atmospheric probe missions to both ice giants. The content is provided for information purposes only. And so, the best guess we have at the moment is that, while it was forming, it collided with something even bigger or as big, and it got knocked over. Saturn is about twice as far away as Jupiter (almost 10 AU) and takes nearly 30 years to complete one orbit. They do have some rocky material, although this is most often found in the planet core. Our own Moon shows evidence of having water ice in deep craters near its south pole. Class V gas giants can be extremely hot, with temperatures above 1400 K (1100 C; 2100 F), or they can be cooler, with lower gravity than Jupiter. So, if you could think about two magnets crossed with each other, it's almost like that. Soon after its launch in 2021, NASA's James Webb Space Telescope will change that by unlocking secrets of the atmospheres of both planets. Internet Explorer). A newly published catalog reveals a fascinating variety of possible exoplanets detected by TESS, the Transiting Exoplanet Survey Satellite. The mysteries of the Uranus system can be unlocked through interdisciplinary exploration. They come in all sizes and orbit a different star. https://en.wikipedia.org/wiki/Saturn Saturn has more than 60 moons, all mostly made of water ice. As with all of the moons of Uranus and Neptune, it is made of ice and rock. Before we can ever send atmospheric probes to the ice giants, we should send one to Saturn. Amy Simon: So, I think I had a two-body gravity assist, actually, the first one being when the shuttle program came around and Sally Ride, I really wanted to be an astronaut, be the first woman on Mars. While the rest of the planets in the solar system move from west to east, Uranus and Venus move from east to west. Could they have acquired a lot of the Kuiper Belt objects as they were doing that? The blue dots on this image show where ice was detected on the Moons south pole.Credit: NASA. Why do astronomers call Uranus and Neptune ice giants? This site is maintained by the Planetary Science Communications team at, https://nasajobs.nasa.gov/studentopps/pathways.htm. Like other gas giants, Uranus is also surrounded by rings. There is never a shortage of worthwhile missions. But the pressure is on to organize a mission in the next decade, because scientists want to take advantage of an approaching planetary alignment that would significantly cut travel time. So, they couldn't pull in quite as much gas. ODU2YzU2ZGY0ZmEyMDc2NWU2NzFjODQ3ODg0ZmViYzJhZjlmY2M5NmRhOGQ5 Your email address is used only to let the recipient know who sent the email. But, perhaps ironically, a high-resolution camera is probably the primary instrument for missions to Uranus and Neptune. . These balls gently collided with each other and formed planetesimals. And we have no way of making it do that. MjU3YjcwYWFkODQxYzcxNmIxNDRhYWVkYWI2YTRjYmY4MzRlNjJhODllNGJj The first four planets from the Sun, Mercury, Venus, Earth, and Mars are terrestrial. The "ice giant" terminology took hold in the 1990s when researchers realized Uranus and Neptune were compositionally different from. But now, the question is - why do these ice giants have different shades of blue. Accessed 5 July, 2023. Given that the newly discovered planet is so far away, astronomers can't actually tell anything about its composition. Amy Simon: Oh, I think we'd find all sorts of interesting things. We've got a lot to learn about Uranus and Neptune and their atmospheres, but more detailed studies with probes will have to wait. https://www.lpi.usra.edu/education/space_days/activities/gasGiants/aboutGasGiants.pdf Phil Davis & Steve Carney Solar power is in short supply in the ice giants' neighborhood. NDI0Yzc5ZmE0MjQ5ZjNiYTczZTliYmJiMzllZjRjNGZmMDM4NTM3MzM0NjBh Interest in the ice giants has grown exponentially, says Amy Simon, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt .