Four Mini-Neptunes found

Newswand: A team of Jananese astronomers has discovered mini-Neptunes around four red dwarfs, which are named TOI-782, TOI-1448, TOI-2120, and TOI-2406, using observations from a global network of ground-based telescopes with MuSCATs and the TESS space telescope.

Photo credit: Astrobiology Center

These four mini-Neptunes are close to their parent stars, and the three of them are likely to be in eccentric orbits (TOI-782 b, TOI-2120 b, TOI-2406 b). These mini-Neptunes are not rocky planets like Earth but may be Neptune-like planets.

The team of astronomers, led by Yasunori Hori and Teruyuki Hirano from Astrobiology Center and Akihiko Fukui and Norio Narita from The University of Tokyo, has reported the discovery and follow-up of four short-period mini-Neptunes around red dwarfs older than one billion years.

At least three of these mini-Neptunes are likely to be in eccentric orbits. The fact that these mini-Neptunes have maintained non-zero eccentricities for billions of years after their birth suggests that they may not be rocky planets like Earth but Neptune-like planets that are less susceptible to tidal deformation. This study should provide a clue to the origins and elusive interior structures of mini-Neptunes.

Planets between the size of Earth and Uranus/Neptune, known as mini-Neptunes, are not found in our Solar System. However, mini-Neptunes are relatively common outside the Solar System and are promising targets for atmospheric characterization by the James Webb Space Telescope.

They have discovered four transiting short-period mini-Neptunes orbiting red dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406) through follow-up observations with ground-based telescopes with MuSCATs (a series of Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets. These mini-Neptunes have radii about 2-3 times that of Earth and orbital periods of less than eight days.

In addition, radial velocity measurements of their parent stars, obtained with the IRD (InfraRed Doppler) on the Subaru telescope, indicate that the upper limit on the masses of these four planets is less than 20 times the mass of Earth. The relationship between the measured radii and the upper mass limits of these mini-Neptunes suggests that they are not rocky planets like Earth. Their interiors likely contain volatiles such as icy materials like H2O and atmospheres.

The team found that at least three of these four mini-Neptunes (TOI-782 b, TOI-2120 b, TOI-2406 b) are likely to be in eccentric orbits. In general, the orbit of a short-period planet around a red dwarf should be circular due to tidal dissipation. However, three short-period mini-Neptunes around red dwarfs have maintained non-zero eccentricities for billions of years. One possible interpretation of this is that their interiors are not susceptible to tidal effects.

Short-period mini-Neptunes are promising targets for atmospheric observations with the James Webb Space Telescope. Further detailed follow-up observations are expected to improve understanding of the internal compositions and atmospheres of short-period mini-Neptunes.

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Exoplanet with SO2 throws new light on planet formation

Newswand: An exoplanet with sulfur dioxide in its atmosphere is helping the astronauts to understand the process of formation of a planet.

Photo creidit: Department of Astronomy, UW–Madison

It is located about 96 light years away from our own solar system and became a prime target for scientists trying to understand how worlds are formed.

Astronomers discovered the planet, GJ 3470 b, in 2012 when the planet’s shadow crossed the star it orbits. GJ 3470 b is located in the constellation Cancer and is about half the size of Neptune, with a mass 10 times that of Earth. In the intervening years, researchers have compiled data on the planet using the Hubble and Spitzer space telescopes, culminating in a pair of recent observations with the James Webb Space Telescope.

They saw evidence of water, carbon dioxide, methane and sulfur dioxide. GJ 3470 b is the lightest and coldest (averaging a mere 325 degrees Celsius, or more than 600 Fahrenheit) exoplanet to harbor sulfur dioxide. The compound is likely a sign of the churn of active chemical reactions in the planet’s atmosphere, created when radiation from its nearby star blasts apart the components of hydrogen sulfide, which then go looking for new molecular partners.

Discovering sulfur dioxide in a planet as small as GJ 3470 b gives one more important item on the planet formation ingredient list, the astronauts opine.

In the case of GJ 3470 b, there are also other interesting features that might help fill out that recipe. The planet’s orbit around its star takes it nearly over the star’s poles, which is to say that it’s circling at a 90-degree angle to the expected path of planets in the system. It’s also surprisingly close to the star, close enough that the light from its star is blowing copious amounts of GJ 3470 b’s atmosphere away into space. The planet has probably lost about 40 percent of its mass since it was formed.

The close-in, off-kilter orbit is a sign that GJ 3470 b used to be somewhere else in its system, and at some point, the planet became entangled with the gravity of another and was pulled into a new path that eventually settled it in a different neighborhood.

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Water frost found for the first time on Mars

Newswand: ESA’s ExoMars and Mars Express missions have spotted water frost for the first time near Mars’s equator, a part of the planet where it was thought impossible for frost to exist.

The frost sits atop the Tharsis volcanoes: the tallest volcanoes not only on Mars but in the Solar System. It was first seen by ESA’s ExoMars Trace Gas Orbiter (TGO), and later by both another instrument aboard TGO and ESA’s Mars Express.

“We thought it was impossible for frost to form around Mars’s equator, as the mix of sunshine and thin atmosphere keeps temperatures relatively high at both surface and mountaintop – unlike what we see on Earth, where you might expect to see frosty peaks,” says lead author Adomas Valantinas, who made the discovery as a PhD student at University of Bern, Switzerland, and is now a postdoctoral researcher at Brown University, USA.

The patches of frost are present for a few hours around sunrise before they evaporate in sunlight. Despite being thin – likely only one-hundredth of a milli metre thick (as thick as a human hair) – they cover a vast area. The amount of frost represents about 150,000 tonnes of water swapping between surface and atmosphere each day during the cold seasons, the equivalent of roughly 60 Olympic swimming pools.

A peculiar microclimate

The Tharsis region of Mars hosts numerous volcanoes, including Olympus Mons and the Tharsis Montes: Ascraeus, Pavonis and Arsia Mons. Many of these volcanoes are colossal, towering above the surrounding plains at heights ranging from one (Pavonis Mons) to three (Olympus Mons) times that of Earth’s Mount Everest.

These volcanoes have calderas, large hollows, at their summits, caused as magma chambers emptied during past eruptions. The researchers propose that air circulates in a peculiar way above Tharsis; this creates a unique microclimate within the calderas of the volcanoes there that allows patches of frost to form.

“Winds travel up the slopes of the mountains, bringing relatively moist air from near the surface up to higher altitudes, where it condenses and settles as frost,” says co-author Nicolas Thomas, Principal Investigator of TGO’s Colour and Stereo Surface Imaging System (CaSSIS) and Adomas’s PhD supervisor at the University of Bern. “We actually see this happening on Earth and other parts of Mars, with the same phenomenon causing the seasonal martian Arsia Mons Elongated Cloud.

Adomas, Nicolas and colleagues spotted frosts on the Tharsis volcanoes of Olympus, Arsia and Ascraeus Mons, and Ceraunius Tholus. Modelling how these frosts form could allow scientists to reveal more of Mars’s remaining secrets, including where water exists and how it moves between reservoirs, and understanding the planet’s complex atmospheric dynamics. Such knowledge is essential for our future exploration of Mars, and our search for possible signs of life beyond Earth.

 “Finding water on the surface of Mars is always exciting, both for scientific interest and for its implications for human and robotic exploration,” says Colin Wilson, ESA project scientist for both ExoMars TGO and Mars Express.

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This exoplanet survives the onslaught of its red giant star

Newswand: A rare exoplanet that should have been stripped down to bare rock by its nearby host star’s intense radiation somehow grew a puffy atmosphere —the latest in a string of discoveries forcing scientists to rethink theories about how planets age and die in extreme environments.

Photo credit: ROBERTO MOLAR CANDANOSA/JOHNS HOPKINS UNIVERSITY

Nicknamed “Phoenix” for its ability to survive its red giant star’s radiant energy, the newly discovered planet illustrates the vast diversity of solar systems and the complexity of planetary evolution—especially at the end of stars’ lives.

“This planet isn’t evolving the way we thought it would. It appears to have a much bigger, less dense atmosphere than we expected for these systems,” said Sam Grunblatt, a Johns Hopkins University astrophysicist who led the research. “How it held on to that atmosphere despite being so close to such a large host star is the big question.”

The new planet belongs to a category of rare worlds called “hot Neptunes” because they share many similarities with the solar system’s outermost, frozen giant despite being far closer to their host stars and far hotter. Officially named TIC365102760 b, the latest puffy planet is surprisingly smaller, older, and hotter than scientists thought possible. It is 6.2 times bigger than Earth, completes an orbit around its parent star every 4.2 days, and is about 6 times closer to its star than Mercury is to the sun.

Because of Phoenix’s age and scorching temperatures, coupled with its unexpectedly low density, the process of stripping its atmosphere must have occurred at a slower pace than scientists thought possible, the scientists concluded. They also estimated that the planet is 60 times less dense than the densest “hot Neptune” discovered to date, and that it won’t survive more than 100 million years before it begins dying by spiraling into its giant star.

“It’s the smallest planet we’ve ever found around one of these red giants, and probably the lowest mass planet orbiting a [red] giant star we’ve ever seen,” Grunblatt said. “That’s why it looks really weird. We don’t know why it still has an atmosphere when other ‘hot Neptunes’ that are much smaller and much denser seem to be losing their atmospheres in much less extreme environments.”

Grunblatt and his team were able to gain such insights by devising a new method for fine-tuning data from NASA’s Transiting Exoplanet Survey Satellite.

Puffy planets are often composed of gases, ice, or other lighter materials that make them overall less dense than any planet in the solar system. They are so rare that scientists believe only about 1% of stars have them. Exoplanets like Phoenix are not as commonly discovered because their smaller sizes make them harder to spot than bigger, denser ones, Grunblatt said.

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