Planet Found in the Habitable Zone of a White Dwarf

An artist’s impression of the white dwarf star WD1054–226 orbited by clouds of planetary debris and a major planet in the habitable zone. Credit Mark A. Garlick / markgarlick.com Licence type Attribution (CC BY 4.0)

Most stars will end their lives as white dwarfs. White dwarfs are the remnant cores of once-luminous stars like our Sun, but they’ve left their lives of fusion behind and no longer generate heat. They’re destined to glow with only their residual energy for billions of years before they eventually fade to black.

Could life eke out an existence on a planet huddled up to one of these fading spectres?

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Rocky Planets Might Need to be the Right age to Support Life

This artist’s impression shows the planet orbiting the 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

Extrasolar planets are being discovered at a rapid rate, with 4,531 planets in 3,363 systems (with another 7,798 candidates awaiting confirmation). Of these, 166 have been identified as rocky planets (aka. “Earth-like”), while another 1,389 have been rocky planets that are several times the size of Earth (“Super-Earths). As more and more discoveries are made, the focus is shifting from the discovery process towards characterization.

In order to place tighter constraints on whether any of these exoplanets are habitable, astronomers and astrobiologists are looking for ways to detect biomarkers and other signs of biological processes. According to a new study, astronomers and astrobiologists should look for indications of a carbon-silicate cycle. On Earth, this cycle ensures that our climate remains stable for eons and could be the key to finding life on other planets.

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Ocean Worlds With Hydrogen-Rich Atmospheres Could be the Perfect Spots for Life

Artist's impression of the surface of a "Hycean" world. Credit: University of Cambridge

The search for planets beyond our Solar System (extrasolar planets) has grown by leaps and bounds in the past decade. A total of 4,514 exoplanets have been confirmed in 3,346 planetary systems, with another 7,721 candidates awaiting confirmation. At present, astrobiologists are largely focused on the “low hanging fruit” approach of looking for exoplanets that are similar in size, mass, and atmospheric composition to Earth (aka. “Earth-like.”)

However, astrobiologists are also interested in finding examples of “exotic life,” the kind that emerged under conditions that are not “Earth-like.” For example, a team of astronomers from the University of Cambridge recently conducted a study that showed how life could emerge on ocean-covered planets with hydrogen-rich atmospheres (aka. “Hycean” planets). These findings could have significant implications for exoplanet studies and the field of astrobiology.

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The Elements for Life Depend on Both how and Where a Planet Forms

Artist's conception of a solar system in formation. Credit: NASA/FUSE/Lynette Cook

In the past few decades, the number of planets discovered beyond our Solar System has grown into the thousands. At present, 4,389 exoplanets have been confirmed in 3,260 systems, with another 5,941 candidates awaiting confirmation. Thanks to numerous follow-up observations and studies, scientists have learned a great deal about the types of planets that exist in our Universe, how planets form, and how they evolve.

A key consideration in all of this is how planets become (and remain) habitable over time. In general, astrobiologists have operated under the assumption that habitability comes down to where a planet orbits within a system – within its parent star’s habitable zone (HZ). However, new research by a team from Rice University, indicates that where a planet forms in its respective star system could be just as important.

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Astronomers are Starting to Find Planets in Much Longer Orbits. Cooler, More Habitable Planets

This artist’s view shows the planet orbiting the young star Beta Pictoris. This exoplanet is the first to have its rotation rate measured. Its eight-hour day corresponds to an equatorial rotation speed of 100 000 kilometres/hour — much faster than any planet in the Solar System.

We’re getting better and better at detecting exoplanets. Using the transit method of detection, the Kepler Space Telescope examined over 530,000 stars and discovered over 2,600 explanets in nine years. TESS, the successor to Kepler, is still active, and has so far identified over 1800 candidate exoplanets, with 46 confirmed.

But what if, hidden in all that data, there were even more planets? Astronomers at Warwick University said they’ve found one of these “lost” planets, and that they think they’ll find even more.

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Astronomers Define the “Really Habitable Zone”. Planets Capable of Producing Gin and Tonic

Gin and tonic. Image Credit: By NotFromUtrecht - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8529628

A hospitable star that doesn’t kill you with deadly flares. A rocky planet with liquid water and an agreeable climate. Absence of apocalyptic asteroid storms. No pantheon of angry, vengeful, and capricious gods. These are the things that define a habitable planet.

Now some scientists are adding one more criterion to the list: gin and tonic.

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Without a Magnetosphere, Planets Orbiting Flare Stars Don’t Stand a Chance

superflare
An artist's conception of a superflare event, on a dwarf star. Image credit: Mark Garlick/University of Warwick

Earthlings are fortunate. Our planet has a robust magnetic shield. Without out magnetosphere, the Sun’s radiation would’ve probably ended life on Earth before it even got going. And our Sun is rather tame, in stellar terms.

What’s it like for exoplanets orbiting more active stars?

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Planet Sizes Matter for Habitability Too.

In order to be considered habitable, a planet needs to have liquid water. Cells, the smallest unit of life, need water to carry out their functions. For liquid water to exist, the temperature of the planet needs to be right. But how about the size of the planet?

Without sufficient mass a planet won’t have enough gravity to hold onto its water. A new study tries to understand how size affects the ability of a planet to hold onto its water, and as a result, its habitability.

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Better Than Earth? Are There Superhabitable Worlds In The Milky Way?

NASA visualization of ocean currents. Credit: NASA/SVS

I’ve said many times in the past that the Earth is the best planet in the Universe. No matter where we go, we’ll never find a planet that’s a better home to Earth life than Earth. Of course, that’s because we, and all other Earth life evolved in this environment. Evolution adapted us to this planet, and it’s unlikely we could ever find another planet this good for us.

However, is it the best planet? Are there places in the Universe which might have the conditions for more diversity of life?

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There Could be Planets Out There Which are Even More Habitable than Earth

Artist’s impression of a Super-Earth planet orbiting a Sun-like star. Credit: ESO/M. Kornmesser

When searching for potentially habitable exoplanets, scientists are forced to take the low-hanging fruit approach. Since Earth is the only planet we know of that is capable of supporting life, this search basically comes down to looking for planets that are “Earth-like”. But what if Earth is not the meter stick for habitability that we all tend to think it is?

That was the subject of a keynote lecture that was recently made at the Goldschmidt Geochemistry Congress, which took place from Aug. 18th to 23rd, in Barcelona, Spain. Here, a team of NASA-supported researchers explained how an examination of what goes into defining habitable zones (HZs) shows that some exoplanets may have better conditions for life to thrive than Earth itself has.

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