Space missions often have to go where the sun don’t shine. Or at least where it shines very faintly. That is particularly important if the mission draws its power from the sun. Luckily, engineers have a way of dealing with that problem – just make really really big solar panels. That is exactly what they did for Lucy, a mission to visit the Trojan asteroids around Jupiter. Those sails have now been tested on the ground, and they are magnificent.
NASA's Hubble Space Telescope snapped this image of the young comet P/2019 LD2 as it orbits near Jupiter's captured ancient asteroids, which are called Trojans. This icy object is the first comet astronomers have spotted near the Trojan population. CREDITS:
NASA, ESA, STScI, B. Bolin (IPAC/Caltech)
Jupiter is notorious for capturing objects that venture too close to the gas giant and its enormous pull of gravity. Asteroids known as Jupiter Trojans are a large group of space rocks that have been snared by the planet, which usually remain in a stable orbit near one of the Jupiter’s Lagrangian points.
But now, the Hubble Space Telescope has spotted a comet near Jupiter’s Trojan asteroid population. This is the first time a comet has been found in this region, and the team of scientists studying the object – named P/2019 LD2 (LD2) – think the unexpected comet is only a temporary visitor.
Artist’s Rendering of Lucy. Credit: Southwest Research Institute
A new study out this month suggests that Jupiter’s Trojan asteroids may be more peculiar than previously thought. The Trojan asteroids are rocky objects which orbit the Sun just ahead of and just behind the gas giant, in gravitational sweet spots known as Lagrange points. The swarm ahead of Jupiter, known as the L4 (Greek) group, is slightly larger than the L5 (Trojan) swarm behind, but until now, astronomers believed that there was otherwise little differentiation between the two swarms. The paper released this month appears to change that.
An artist’s conception of the Lucy spacecraft (left) flying by the Trojan Eurybates, and Psyche (Right) Psyche, the first mission to the metal world 16 Psyche.
Credits: SwRI and SSL/Peter Rubin
It’s a New Year, with new challenges and new opportunities! And NASA, looking to kick things off, has announced the two new missions that will be launching in the coming decade. These robotic missions, named Lucy and Psyche, are intended to help us understand the history of the early Solar System, and will deploy starting in 2021 and 2023, respectively.
While Lucy’s mission is to explore one of Jupiter’s Trojan asteroids, Psyche will explore a metal asteroid known as 16 Psyche. And between the two of them, it is hoped that they will answer some enduring questions about planetary formation and how the Solar System came to be. More than that, these mission represent historic firsts for NASA and human space exploration.
NASA’s Discovery Program, of which Lucy and Psyche are part, was created in 1992 to compliment their larger “flagship” programs. By bringing scientists and engineers together to design missions, the Discovery Program’s focus has been to maximize scientific research by creating many smaller missions that have shorter development periods and require less in the way of operational resources.
Artist’s concept of the Lucy spacecraft flying by Eurybates, one of the six diverse and scientifically important Trojans it will study. Credit: SwRI
The Lucy mission is scheduled to launch in October of 2021, and is expected to arrive at its first destination (a Main Belt asteroid) in 2025. It will then set course for Jupiter’s Trojans, a group of asteroids that are trapped by Jupiter’s gravity and share its orbit. These asteroids are thought to be relics of the early Solar System; and between 2027 and 2033, Lucy will study six of them.
In addition to being the first mission to explore Jupiter’s Trojan population, Lucy is also of historic importance because of the number of asteroids it will visit. Throughout the course of its mission, it is will investigate six Trojans, which is the total number of Main Belt asteroids that have been studied to date. The nature of these six asteroids is also expected to tell us much about the early history of the Solar System.
As Harold F. Levison – the principal investigator of the Lucy mission from the Southwest Research Institute (SwRI) in Boulder, Colorado – explained during a NASA call-in briefing:
“One of the surprising aspects of this population is their diversity. If we look at them through telescopes on the Earth, we see that they are very different from one other in their color, in their spectra. And so, we believe that’s telling us something about how the Solar System formed and evolved… This diversity in these objects, we believe, are due to the fact that they actually formed in very different regions of the Solar System, with very different physical characteristics. And something occurred in the history of the Solar System where these objects started off at very different distances, but during the formation and evolution of the Solar System, they got moved around and placed in these stable reservoirs near Jupiter’s orbit.”
Illustration of the Lucy spacecraft’s orbit around Jupiter, which will allow it to study its Trojan population. Credit: SwRI
The six Trojans that Lucy is intended investigate were selected because the diversity of their physical characteristics show that they are from different locations throughout the Solar System. As Levison put it, “These small bodies really are the fossils of planet formation, and that’s why we named Lucy after the human ancestor known as Lucy.”
In addition, Lucy will build on the success of missions like New Horizons and OSIRIS-REx., which includes using updated versions of instruments they used to explore Pluto, the Kuiper Belt, and the asteroid Bennu -i.e. the RALPH and LORRI instruments and the OTES instrument. In addition, several members of the New Horizons and OSIRIS-REx science teams will be lending their expertise to the Lucy mission.
Similarly, the Psyche mission will of be immense scientific value since it will visit the only metal asteroid known to exist. This asteroid measures about 210 km (130 mi) in diameter and is believed to be composed entirely of iron and nickel. In this respect, it is similar to Earth’s metallic core, as well as the cores of every terrestrial planet in the Solar System.
It is for this reason why scientists believe it may be the exposed core of a Mars-sized planet. According to this theory, 16 Psyche experienced several major collisions during the early history of the Solar System, which caused it to shed its rocky mantle. The robotic probe will launch in 2023 and is expected to arrive by 2030 – after receiving an Earth gravity-assist maneuver in 2024 and a Mars flyby in 2025.
By measuring its composition, magnetic field, and mapping its surface features, Lucy’s science team hopes to learn more about the history of planetary formation. As Lindy Elkins-Tanton – the Principal Investigator of Psyche and the Director of the School of Earth and Space Exploration at Arizona State University – said during the NASA call-in briefing:
“Humankind has visited rocky worlds and icy worlds and worlds made of gas. But we have never seen a metal world. Psyche has never been visited or had a picture taken that was more than a point of light. And so, its appearance remains a mystery. This mission will be true exploration and discovery. We think that Psyche is the metal core of a small planet that was destroyed in the high-energy, high-speed, first one-one-hundredth of the age of our Solar System. By visiting Psyche we can literally visit a planetary core the only way humanity can… Psyche let’s us visit inner space by visiting outer space.”
Not only are planetary cores thought to be where magnetic fields originate (which are necessary for the emergence of life), but they are entirely inaccessible to us. The very edge of Earth’s outer core is roughly 2,890 km (1790 mi) from our planet’s surface. But the deepest humanity has ever dug has been to a depth of 12 km (7.5 mi), which took place at the Kola Superdeep Borehole, in Russia.
In addition, within the Earth’s core, temperature and pressure conditions are estimated to reach 5700 K (5400 °C; 9752 °F) and 330 to 360 gigapascals (over three million times normal air pressure). This makes exploring the core of our planet (or any other planet in the Solar System, for that matter) completely impractical. Hence why a robotic mission to a world like Pysche is such an opportunity.
And since Psyche is the only rounded body of metal that is known to exist in the Solar System, the asteroid is as improbably as it is unique. And since no missions have ever taken place to explore its surface, and no pictures exist that can tell us what its surface features would look like, the Psyche mission is sure to shed some serious light on what a metal world looks like.
“What do we think it might look like?” asked Tanton. “Does it have surface sulfur lava flows on its surface? Is it covered with towering cliffs created when solidifying metal shrank and the exterior of the body broke into fault? Is its surface a combination of iron metal and green mineral crystal as iron meteorites are? And what does an impact crater in metal look like? Could its edges or its metal flashes become frozen in the cold of space before they fell back on the surface. We don’t know.”
Jim Green, NASA’s Planetary Science Director, expressed enthusiasm for the Discovery 13 and 14 missions in a recent NASA press release:
“These are true missions of discovery that integrate into NASA’s larger strategy of investigating how the solar system formed and evolved. We’ve explored terrestrial planets, gas giants, and a range of other bodies orbiting the sun. Lucy will observe primitive remnants from farther out in the solar system, while Psyche will directly observe the interior of a planetary body. These additional pieces of the puzzle will help us understand how the sun and its family of planets formed, changed over time, and became places where life could develop and be sustained – and what the future may hold.”
Lucy and Psyche were chosen from five finalists that were selected for further development back in September 2015. These in turn were chosen from 27 mission concepts that were submitted back in November of 2014. Examples of past and present Discovery missions include the Kepler space probe, the Dawn spacecraft, the Mars Pathfinder, and the InSight lander (which is scheduled to launch in 2018).
Lucy, an SwRI mission proposal to study primitive asteroids orbiting near Jupiter, is one of five science investigations under the NASA Discovery Program up for possible funding. Credit: swri.org
In February of 2014, NASA’s Discovery Program put out the call for mission proposals, one or two of which will have the honor of taking part in Discovery Mission Thirteen. Hoping to focus the next round of exploration efforts to places other than Mars, the five semifinalists (which were announced this past September) include proposed missions to Venus, Near-Earth Objects, and asteroids.
When it comes to asteroid exploration, one of the possible contenders is Lucy – a proposed reconnaissance orbiter that would study Jupiter‘s Trojan Asteroids. In addition to being the first mission of its kind, examining the Trojans Asteroids could also lead to several scientific finds that will help us to better understand the history of the Solar System.
By definition, Trojan are populations of asteroids that share their orbit with other planets or moons, but do not collide with it because they orbit in one of the two Lagrangian points of stability. The most significant population of Trojans in the Solar System are Jupiter’s, with a total of 6,178 having been found as of January 2015. In accordance with astronomical conventions, objects found in this population are named after mythical figures from the Trojan War.
There are two main theories as to where Jupiter’s Trojans came from. The first suggests that they formed in the same part of the Solar System as Jupiter and were caught by the gas giant’s gravity as it accumulated hydrogen and helium from the protoplanetary disk. Since they would have shared the same approximate orbit as the forming gas giant, they would have been caught in its gravity and orbited it ever since.
The asteroids of the Inner Solar System and Jupiter. Credit: Wikipedia Commons
The second theory, part of the Nice model, proposes that the Jupiter Trojans were captured about 500-600 million years after the Solar System’s formation. During this period Uranus, Neptune – and to a lesser extent, Saturn – moved outward, whereas Jupiter moved slightly inward. This migration could have destabilized the primordial Kuiper Belt, throwing millions of objects into the inner Solar System, some of which Jupiter then captured.
In either case, the presence of Trojan asteroids around Jupiter can be traced back to the early Solar System. Studying them therefore presents an opportunity to learn more about its history and formation. And if in fact the Trojans are migrant from the Kuiper Belt, it would also be a chance for scientists to learn more about the most distant reaches of the solar system without having to send a mission all the way out there.
The mission would be led by Harold Levison of the Southwest Research Institute (SwRI) in Boulder, Colorado, with the Goddard Space Center managing the project. Its targets would most likely include asteroid (3548) Eurybates, (21900) 1999 VQ10, (11351) 1997 TS25, and the binary (617) Patroclus/Menoetius. It would also visit a main-belt asteroid (1981 EQ5) on the way.
The spacecraft would perform scans of the asteroids and determine their geology, surface features, compositions, masses and densities using a sophisticated suite of remote-sensing and radio instruments. In addition, during it’s proposed 11-year mission, Lucy would also gather information on the asteroids thermal and other physical properties from close range.
Artist’s concept of Jupiter’s Trojan asteroids hovering in the foreground in Jupiter’s path, with the “Greeks” at left in the background. Credit: NASA.
The project is named Lucy in honor of one of the most influential human fossils found on Earth. Discovered in the Awash Valley of Ethiopia in 1974, Lucy’s remains – several hundred bone fragments that belonged to a member the hominid species of Australopithecus afarensis – proved to be an extraordinary find that advanced our knowledge of hominid species evolution.
Levison and his team are hoping that a similar find can be made using the probe of the same name. As he and his colleagues describe it, the Lucy mission is aimed at “Surveying the diversity of Trojan asteroids: The fossils of planet formation.”
“This is a once-in-a-lifetime opportunity,” said Levinson. “Because the Trojan asteroids are remnants of that primordial material, they hold vital clues to deciphering the history of the solar system. These asteroids are in an area that really is the last population of objects in the solar system to be visited.”
The payload is expected to include three complementary imaging and mapping instruments, including a color imaging and infrared mapping spectrometer, a high-resolution visible imager, and a thermal infrared spectrometer. NASA has also offered an additional $5 to $30 million in funding if mission planners choose to incorporate a laser communications system, a 3D woven heat shield, a Deep Space atomic clock, and/or ion engines.
As one of the semifinalists, the Lucy mission has received $3 million dollars to conduct concept design studies and analyses over the course of the next year. After a detailed review and evaluation of the concept studies, NASA will make the final selections by September 2016. In the end, one or two missions will receive the mission’s budget of $450 million (not including launch vehicle funding or post-launch operations) and will be launched by 2020 at the earliest.
