- 3588 - NEPTUNE and URANUS - spacecraft to visit? - Uranus is the least-explored planet of our solar system alongside Neptune. Understanding how and where these two planets formed has direct implications for the evolution of our own planet.
----------- 3588 - NEPTUNE and URANUS - spacecraft to visit?
- Earth formed about 4,600,000,000 years ago as a result of a violent process where thousands of baby planets over 62 miles diameter in size collided with each other and accreted over a few million years. Scientists think early Earth would have lost most of its water to space due to the high heat from this process.
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- Our water instead likely came during a brief period roughly 4 billion years ago when the grand migration of the giant planets of our solar system, Jupiter, Saturn, Uranus and Neptune, scattered large asteroids and comets all over. Many of these bombarded Earth, depositing water and organic materials which are essential ingredients for life as we know it.
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- Yet beyond the existence of such a critical period we don’t know exactly how the giant planets formed, how they migrated and where from. What's the difference between gas giants and ice giants?
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- Jupiter and Saturn (the gas giants) and Uranus and Neptune (the ice giants) represent two different classes of planets. The gas giants are primarily made up of hydrogen and helium; ice giants contain those substances as well as heavier ones such as oxygen, nitrogen, carbon and sulfur. While their cores were forged from rapidly accreting rock-metal baby planets in the outer disk of material surrounding the Sun, their outer layers accumulated differently.
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- Since Jupiter and Saturn were the first and most massive planets to form, they gobbled up most of the outer solar disk’s hydrogen and helium to create their mantles and outer atmospheres. This left the still-growing mantles of Uranus and Neptune with more fractions of ices like water and ammonia, and only a relatively thin hydrogen and helium atmosphere.
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- Figuring out the origin of ice giants is key to understanding not only our own solar system but countless others across the galaxy. Even though planets around other stars are incredibly far away, astronomers can use certain techniques to infer their masses and sizes, and thus their densities, to tell a gas giant apart from an icy one.
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- In the thousands of exoplanets discovered to date (> 5,000), Uranus- and Neptune-scale worlds are the most common, followed by the gas giants. The giant planets are thus key to understanding planetary formation across the Universe.
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- Clues to the origin and evolution of giant planets lie in the specific elements that make up their atmospheres, ones other than the hydrogen were inherited from the Sun’s disk. For example, noble gases like helium undergo very few chemical reactions inside giant planets so measuring their abundance compared to other gases will tell scientists how and where each planet acquired its heavy elements over time.
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- The trouble is that other than the direct gas measurements from inside Jupiter’s atmosphere by NASA’s Galileo probe in 1995, we lack such information on Saturn, Uranus and Neptune. This is particularly pressing for the ice giants because their noble gases are the most unaltered reflections of the planet-forming materials in the early outer solar disk.
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- Neptune and Uranus are the least-explored planets of our solar system, only flown past once by NASA’s Voyager 2 spacecraft in the last century, which also flew by Jupiter and Saturn.
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- The most recent gravity data from NASA’s Juno spacecraft, which entered Jovian orbit in 2016, provided evidence that Jupiter doesn’t have a distinct rock-metal core. Jupiter's core is larger and fuzzier than expected, likely caused by the intense gas pressures in its mantle dissolving the core into an exotic substance called “metallic hydrogen“, or due to Jupiter absorbing a planet with 10 Earth masses during its formation.
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- Data from NASA’s Cassini mission suggests Saturn has a fuzzy core too, spanning 60% of the planet’s diameter. These discoveries have led scientists to think that Uranus and Neptune might also have large diluted cores. The only way to know is to send a mission to the ice giants.
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- The 2023-2032 Planetary Science Decadal Survey produced every 10 years by the U.S. scientific community to guide future NASA missions recommends sending a spacecraft to Uranus as the highest priority.
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- If commissioned, the “Uranus Orbiter and Probe” (UOP) mission will measure the planet’s complex and unique magnetic field, map gravity variations, and note the nature of its atmospheric wobbles to determine if the planet really sports a fuzzy core and what it is made of. A probe would enter Uranus’ atmosphere and precisely measure gases and their relative abundance.
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- The UOP mission would thus paint us a clear picture of where and how Uranus formed, and how it subsequently evolved. Because of the two ice giants' similarity, these insights would also likely apply to Neptune.
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- The mission would also provide us with missing information necessary to understand the migration of the gas giants and the connected evolution of our solar system and early Earth.
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- The UOP could launch on a SpaceX Falcon Heavy rocket in 2031 or 2032 and reach Uranus 12 to 13 years later.
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- ESA is also considering a Uranus orbiter mission. China is considering a Voyager-like mission to interstellar space that would launch in 2024 and fly past Neptune in 2038. The spacecraft would include an atmospheric probe.
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- In the meanwhile, observing Jupiter-like and Neptune-like planets in different star systems lets us witness snapshots of planets forming, migrating and evolving. The next generation of telescopes, like the “Nancy Grace Roman Space Telescope“, will advance such studies by letting us observe ice giant worlds in various stages of formation.
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- The ice giants in our backyard are essential to understanding how planets form and evolve. It’s time we give them a visit.
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May 27, 2022 NEPTUNE and URANUS - spacecraft to visit? 3588
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