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.
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.
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.
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?
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?
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.
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.
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.
One of the great things about science is that it builds on itself over time. Data collected decades ago is still valid and helps scientists spot trends that would otherwise be lost in the flurry of new data they are trying to collect. And sometimes, that data holds something interesting. Such is the case when a group of scientists took a look at the infrared data of Neptune’s atmosphere and found not one but two weird changes happening.
The outer “ice giant” planets, Neptune and Uranus, have plenty of mysteries. One of the biggest is where exactly they got their magnetic fields. They are strong at that, with Neptune’s being twenty-seven times more powerful than Earth’s, while Uranus’ varies between ? and four times Earth’s strength. Chaos rules in these electromagnetic environments, making them exceptionally hard to both understand and model. Now a team of researchers led by Dr. Vitali Prakpenka of the University of Chicago thinks they might have found the underlying cause of both the field’s strength and its randomness – “hot ice.”