Webb Reveals Secrets of Neptune’s Evolution

JWST's view of Neptune in infrared. The telescope also studied the surfaces of two icy asteroids in the Kuiper Belt that lie beyond Neptune. Courtesy: NASA, ESA, CSA, STScI
JWST's view of Neptune in infrared. The telescope also studied the surfaces of two icy asteroids in the Kuiper Belt that lie beyond Neptune. Courtesy: NASA, ESA, CSA, STScI

A twinset of icy asteroids called Mors-Somnus is giving planetary scientists some clues about the origin and evolution of objects in the Kuiper Belt. JWST studied them during its first cycle of observations and revealed details about their surfaces, which gives hints at their origins. That information may also end up explaining how Neptune got to be the way it is today.

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Uranus and Neptune are Actually Pretty Much the Same Color

Scientists reprocessed Voyager 2 images to get the "true" colors of Uranus and Neptune. Turns out they're a pretty blueish-green. Courtesy NASA/Irwin, et al, Anton Pozdnyakov.
Scientists reprocessed Voyager 2 images to get the "true" colors of Uranus and Neptune. Turns out they're a pretty blueish-green. Courtesy NASA/Irwin, et al, Anton Pozdnyakov.

In the late 1980s, the Voyager 2 spacecraft snapped the “canonical” up-close images of Uranus and Neptune. In those views, Uranus was a pretty greenish-blue and Neptune appeared a deep azure color. It turns out that both planets are pretty close in color: a greenish-blue more akin to Uranus’s appearance.

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Aerocapture is a Free Lunch in Space Exploration

Visualisation of the ExoMars Trace Gas Orbiter aerobraking at Mars. Credit: ESA/ATG medialab.

This article was updated on 11/28/23

When spacecraft return to Earth, they don’t need to shed all their velocity by firing retro-rockets. Instead, they use the atmosphere as a brake to slow down for a soft landing. Every planet in the Solar System except Mercury has enough of an atmosphere to allow aerocapture maneuvers, and could allow high-speed exploration missions. A new paper looks at the different worlds and how a spacecraft must fly to take advantage of this “free lunch” to slow down at the destination.

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Want to Explore Neptune? Use Triton’s Atmosphere to Put on the Brakes

Aerobraking is commonly used to slow down spacecraft when they arrive at various planetary systems. It requires a spacecraft to dip into the atmosphere of a celestial body in the planetary system, such as a moon or the planet itself, and use the resistance from that atmosphere to shed some of its velocity. That slow-down would then allow it to enter an orbit in the planetary system without carrying the extra fuel required to do the maneuvers through powered flight, thereby saving weight on the mission and reducing its cost.  

Unfortunately, saying the orbital dynamics of such a maneuver are complicated is an understatement. But ultimately, for any aerobraking to be viable, someone has to do the math. And that’s just what Jakob Brisby and James Lyne, a graduate student and professor at the University of Tennessee Knoxville, did for some of the least visited planetary systems in the solar system – Neptune.

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Neptune's Cloud Cover is Linked to the Solar Cycle

This sequence of Hubble Space Telescope images chronicles the waxing and waning of the amount of cloud cover on Neptune. Credits: NASA, ESA, Erandi Chavez (UC Berkeley), Imke de Pater (UC Berkeley)

Whenever Neptune reaches its closest point in the sky to Earth, its portrait is taken by the Hubble Space Telescope and other ground-based observatories. Watching the planet from 1994 to 2020, astronomers have made puzzling discovery.

The clouds in Neptune’s atmosphere appear to be to be linked to the solar cycle and not the planet’s cycle of seasons. The global cloud cover seems to come and go in a cycle that apparently syncs up with the Sun’s 11-year cycle, as it shifts from solar maximum to solar minimum or vice versa. This is surprising since Neptune is so far from the Sun and receives about 0.1% of Earth’s sunlight.

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Scientists Examine Geological Processes of Monad Regio on Neptune’s Largest Moon, Triton

Global color mosaic of Neptune's largest moon, Triton, taken by NASA's Voyager 2 in 1989. (Credit: NASA/JPL-Caltech/USGS)

In a recent study submitted to the journal Icarus, a team of researchers at the International Research School of Planetary Science (IRSPS) located at the D’Annunzio University of Chieti-Pescara in Italy conducted a geological analysis of a region on Neptune’s largest moon, Triton, known as Monad Regio to ascertain the geological processes responsible for shaping its surface during its history, and possibly today. These include what are known as endogenic and exogenic processes, which constitute geologic processes occurring internally (endo-) and externally (exo-) on a celestial body. So, what new insights into planetary geologic processes can we learn from this examination of Monad Regio?

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Will Triton finally answer, ‘Are we alone?’

NASA’s Voyager 2 took this global color mosaic of Neptune’s largest moon, Triton, in 1989. (Credit: NASA/NASA-JPL/USGS)

We recently examined how and why Saturn’s icy moon, Enceladus, could answer the longstanding question: Are we alone? With its interior ocean and geysers of water ice that shoot out tens of kilometers into space that allegedly contains the ingredients for life, this small moon could be a prime target for future astrobiology missions. But Enceladus isn’t the only location in our solar system with active geysers, as another small moon near the edge of the solar system shares similar characteristics, as well. This is Neptune’s largest moon, Triton, which has been visited only once by NASA’s Voyager 2 in 1989. But are Triton’s geysers the only characteristics that make it a good target for astrobiology and finding life beyond Earth?

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China is Considering a Nuclear-Powered Mission to Neptune

Artist's impression of what the surface of Triton may look like. Credit: ESO

One look at the Planetary Decadal Survey for 2023 – 2032, and you will see some bold and cutting-edge mission proposals for the coming decade. Examples include a Uranus Orbiter and Probe (UOP) that would study Uranus’ interior, atmosphere, magnetosphere, satellites, and rings; and an Enceladus orbiter and surface lander to study the active plumes emanating from Enceladus’ southern polar region. Not to be outdone, China is also considering a nuclear-powered Neptune Explorer to explore the ice giant, its largest moon (Triton), and its other satellites and rings.

The mission was the subject of a study conducted by researchers from the China National Space Agency (CNSA), the Chinese Academy of Sciences (CAS), the China Atomic Energy Authority, the China Academy of Space Technology, and multiple universities and institutes. The paper that describes their findings (published in the journal Scientia Sinica Technologica) was led by Guobin Yu, a researcher with the School of Astronautics at Beihang University and the Department of Science and Technology and Quality at the CNSA.

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The Rings of Uranus and Neptune Could Help map Their Interiors

Mapping the interior of the ice giants is difficult, to say the least. Not only are they far away and therefore harder to observe, but their constant ice cover makes it extremely hard to detect what lies underneath. So scientists must devise more ingenious ways to see what’s inside them. A team from the University of Idaho, Cal Tech, Reed College, and the University of Arizona think they might have come up with a way – to look at the structure of Neptunes’ and Uranus’ rings.

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Why are Uranus and Neptune Different Colors? Haze

NASA’s Voyager 2 spacecraft captured these views of Uranus (on the left) and Neptune (on the right) during its flybys of the planets in the 1980s.

Way back in the late 1980s, the Voyager 2 spacecraft visited Uranus and Neptune. During the flybys, we got to see the first close-up views of those ice giants. Even then, planetary scientists noticed a marked color difference between the two. Yes, they both sport shades of blue. But, if you look closely at Uranus, you see a featureless pale blue planet. Neptune, on the other hand, boasts interesting clouds, dark banding, and dark spots that come and go. They’re all set against a darker blue backdrop.

So, why the difference? Planetary scientists have long suspected aerosols (droplets of gas that have liquids or dust suspended in them) in each atmosphere. But, according to a team of scientists studying the layers of the planets, the hazes those aerosols create may only be part of the story.

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