A Mini-Neptune in the Habitable Zone in a Binary Star System

Sometimes, it seems like habitable worlds can pop up almost anywhere in the universe. A recent paper from a team of citizen scientists led by researchers at the Flatiron Institute might have found an excellent candidate to look for one – on a moon orbiting a mini-Neptune orbiting a star that is also orbited by another star.

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A New Venus-Sized World Found in the Habitable Zone of its Star

The parade of interesting new exoplanets continues. Today, NASA issued a press release announcing the discovery of a new exoplanet in the Gliese 12 system, sized somewhere between Earth and Venus and inside the host star’s habitable zone. Two papers detail the discovery, but both teams think that the planet is an excellent candidate for follow-up with the James Webb Space Telescope (JWST) to try to tease out whether it has an atmosphere and, if so, what that atmosphere is made of.

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The Seven Most Intriguing Worlds to Search for Advanced Civilizations (So Far)

Sometimes, the easy calculations are the most interesting. A recent paper from Balázs Bradák of Kobe University in Japan is a case in point. In it, he takes an admittedly simplistic approach but comes up with seven known exoplanets that could hold the key to the biggest question of them all – are we alone?

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Did the Galileo Mission Find Life on Earth?

An image of Earth taken by the Galileo spacecraft in 1990. Credit: NASA/JPL

In the Fall of 1989, the Galileo spacecraft was launched into space, bound for Jupiter and its family of moons. Given the great distance to the king of planets, Galileo had to take a roundabout tour through the inner solar system, making a flyby of Venus in 1990 and Earth in 1990 and 1992 just to gain enough speed to reach Jupiter. During the flybys of Earth Galileo took several images of our planet, which astronomers have used to discover life on Earth.

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The Combination of Oxygen and Methane Could Reveal the Presence of Life on Another World

This artist’s impression shows a Super-Earth orbiting a Sun-like star. HD 85512 in the southern constellation of Vela (The Sail). This planet is one of sixteen super-Earths discovered by the HARPS instrument on the 3.6-metre telescope at ESO’s La Silla Observatory. This planet is about 3.6 times as massive as the Earth lis at the edge of the habitable zone around the star, where liquid water, and perhaps even life, could potentially exist. Credit: ESO

In searching for life in the Universe, a field known as astrobiology, scientists rely on Earth as a template for biological and evolutionary processes. This includes searching for Earth analogs, rocky planets that orbit within their parent star’s habitable zone (HZ) and have atmospheres composed of nitrogen, oxygen, and carbon dioxide. However, Earth’s atmosphere has evolved considerably over time from a toxic plume of nitrogen, carbon dioxide, and traces of volcanic gas. Over time, the emergence of photosynthetic organisms caused a transition, leading to the atmosphere we see today.

The last 500 million years, known as the Phanerozoic Eon, have been particularly significant for the evolution of Earth’s atmosphere and terrestrial species. This period saw a significant rise in oxygen content and the emergence of animals, dinosaurs, and embryophyta (land plants). Unfortunately, the resulting transmission spectra are missing in our search for signs of life in exoplanet atmospheres. To address this gap, a team of Cornell researchers created a simulation of the atmosphere during the Phanerozoic Eon, which could have significant implications in the search for life on extrasolar planets.

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Chinese Scientists Complete a Concept Study for a 6-Meter Space Telescope to Find Habitable Exoplanets

Illustration of the proposed Tainlin Spacecraft. Credit: CNSA

We have discovered more than 5,400 planets in the universe. These worlds range from hot jovians that closely orbit their star to warm ocean worlds to cold gas giants. While we know they are there, we don’t know much about them. Characteristics such as mass and size are fairly straightforward to measure, but other properties such as temperature and atmospheric composition are more difficult. So the next generation of telescopes will try to capture that information, including one proposed telescope from the Chinese National Space Administration.

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A New Place to Search for Habitable Planets: “The Soot Line.”

Artist impression of a young planet-forming disk illustrating the respective locations of the soot and water-ice lines. Planets born interior to the soot line will be silicate-rich. Planets born interior to the water-ice line, but exterior to the soot line will be silicate and soot-rich (“Sooty Worlds”). Planets born exterior to the water-ice line will be water worlds. Image credit: Ari Gea/SayoStudio.

The habitable zone is the region around a star where planets can maintain liquid water on their surface. It’s axiomatic that planets with liquid water are the best places to look for life, and astronomers focus their search on that zone. As far as we can tell, no water equals no life.

But new research suggests another delineation in solar systems that could influence habitability: The Soot Line.

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Do Red Dwarfs Provide Enough Sunlight for Plants to Grow?

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface. Credit: ESO/M. Kornmesser

To date, 5,250 extrasolar planets have been confirmed in 3,921 systems, with another 9,208 candidates awaiting confirmation. Of these, 195 planets have been identified as “terrestrial” (or “Earth-like“), meaning that they are similar in size, mass, and composition to Earth. Interestingly, many of these planets have been found orbiting within the circumsolar habitable zones (aka. “Goldilocks zone”) of M-type red dwarf stars. Examples include the closest exoplanet to the Solar System (Proxima b) and the seven-planet system of TRAPPIST-1.

These discoveries have further fueled the debate of whether or not these planets could be “potentially-habitable,” with arguments emphasizing everything from tidal locking, flare activity, the presence of water, too much water (i.e., “water worlds“), and more. In a new study from the University of Padua, a team of astrobiologists simulated how photosynthetic organisms (cyanobacteria) would fare on a planet orbiting a red dwarf. Their results experimentally demonstrated that oxygen photosynthesis could occur under red suns, which is good news for those looking for life beyond Earth!

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Maybe There’s No Way to Tell if Habitable Planets Orbit Proxima Centauri… Yet!

This artist’s impression shows the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface. Credit: ESO/M. Kornmesser

Our closest stellar neighbor is Proxima Centauri, an M-type (red dwarf) star located over 4.24 light-years away (part of the Alpha Centauri trinary system). In 2016, the astronomical community was astounded to learn that an Earth-like planet orbited within this star’s circumsolar habitable zone (HZ). In addition to being the closest exoplanet to Earth, Proxima b was also considered the most promising place to look for extraterrestrial life for a time.

Unfortunately, the scientific community has been divided on whether or not life could even be possible on this planet. All of these studies indicate that this question cannot be answered until astronomers characterize Proxima b’s atmosphere, ideally by observing it as it passes in front (aka. transited) of its host star. But in a new NASA-supported study, a team led by astrophysicists at the University of Chicago determined that this is an unlikely possibility.

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Most Exoplanets won’t Receive Enough Radiation to Support an Earth-Like Biosphere

Earth as seen by the JUNO spacecraft in 2013. Credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill.

To date, astronomers have confirmed the existence of 4,422 extrasolar planets in 3,280 star systems, with an additional 7,445 candidates awaiting confirmation. Of these, only a small fraction (165) have been terrestrial (aka. rocky) in nature and comparable in size to Earth – i.e., not “Super-Earths.” And even less have been found that are orbiting within their parent star’s circumsolar habitable zone (HZ).

In the coming years, this is likely to change when next-generation instruments (like James Webb) are able to observe smaller planets that orbit closer to their stars (which is where Earth-like planets are more likely to reside). However, according to a new study by researchers from the University of Napoli and the Italian National Institute of Astrophysics (INAF), Earth-like biospheres may be very rare for exoplanets.

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