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takyon writes:

Last week, news of the discovery of a potentially habitable "Earth-like" exoplanet orbiting the nearest star to our Sun (Proxima Centauri) leaked to Der Spiegel. Today, the European Southern Observatory confirmed the news about Proxima b:

Astronomers using ESO telescopes and other facilities have found clear evidence of a planet orbiting the closest star to Earth, Proxima Centauri. The long-sought world, designated Proxima b, orbits its cool red parent star every 11 days and has a temperature suitable for liquid water to exist on its surface. This rocky world is a little more massive than the Earth and is the closest exoplanet to us — and it may also be the closest possible abode for life outside the Solar System. A paper describing this milestone finding will be published in the journal Nature on 25 August 2016.

[...] At times Proxima Centauri is approaching Earth at about 5 kilometres per hour — normal human walking pace — and at times receding at the same speed. This regular pattern of changing radial velocities repeats with a period of 11.2 days. Careful analysis of the resulting tiny Doppler shifts showed that they indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about 7 million kilometres from Proxima Centauri — only 5% of the Earth-Sun distance.

A note on the press release discusses the potential habitability of Proxima b, given that it is orbiting close to a red dwarf star:

[Continues...]

takyon writes:

Researchers have calculated that Proxima b may have liquid water oceans on its surface, or even be an "ocean planet" based on larger estimates of its radius:

A rocky planet discovered in the "habitable" zone of the star nearest our Sun may be covered with oceans, researchers at France's CNRS research institute said Thursday. A team including CNRS astrophysicists have calculated the size and surface properties of the planet dubbed Proxima b, and concluded it may be an "ocean planet" similar to Earth.

[...] They calculated the radius was between 0.94 and 1.4 times that of Earth, which is 6,371 kilometres on average. Assuming a minimum radius of 5,990 km, the planet would be very dense, with a metallic core making up two-thirds of the entire planet's mass, surrounded by a rocky mantle. If there is surface water, it would not contribute more than 0.05 percent to the planet's total mass, the team said—similar to Earth, where it is about 0.02 percent.

In the larger planet scenario, with a radius of 8,920 km, Proxima b's mass would be split 50-50 between a rocky centre and surrounding water. "In this case, Proxima b would be covered by a single, liquid ocean 200 km deep," said the CNRS. "In both cases, a thin, gassy atmosphere could surround the planet, like on Earth, rendering Proxima b potentially habitable," it concluded.

The exoplanet has not been seen transiting Proxima Centauri, so further data about its size and composition will require the James Webb Space Telescope or other observatories to directly observe it.

Original article in French.

Previously: "Earth-Like" Exoplanet Found in Habitable Zone of Proxima Centauri
ESO Confirms Reports of Proxima Centauri Exoplanet

Original Submission

takyon writes:

Astronomers have observed enough planetary transits to confirm the existence of seven "Earth-sized" exoplanets orbiting TRAPPIST-1, an ultra-cool (~2550 K) red dwarf star about 39.5 light years away. Three of the exoplanets are located inside the "habitable zone" of their parent star. These three orbit from 0.028 to 0.045 AU away from the star:

Astronomers using the TRAPPIST–South telescope at ESO's La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world, have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth.

The exoplanets are presumed to be tidally locked. The six closest to TRAPPIST-1 have been determined to be rocky, while the seventh, TRAPPIST-1h, requires additional observations to determine its characteristics due to its longer orbital period.

Mass estimates for the planets range from 0.41 Earth masses (M_⊕) to 1.38 M_⊕. Radii range from 0.76 Earth radii (R_⊕) to 1.13 R_⊕.

Spitzer, Hubble, and other telescopes will continue to make observations of the TRAPPIST-1 planetary system, but the best data will likely come from the James Webb Space Telescope (JWST), which is scheduled to launch in late 2018. JWST will allow the atmospheres and temperatures of many exoplanets to be characterized, which will help to settle whether the "habitable zones" of red dwarf stars are actually hospitable.

Artist illustrations and data for the TRAPPIST-1 system compared to Mercury, Venus, Mars, and Earth.

Here's a website dedicated to the star.

Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1 (DOI: 10.1038/nature21360) (DX)

Original Submission

kaszz writes:

A exoplanet has been discovered (paywalled) that is called "LHS 1140b" and it's deemed a super earth. It lies in the Goldilocks zone where water is in an accessible fluid phase. The atmosphere, however, also plays a critical role, as can be demonstrated with the planet Venus. Seven exoplanets had been found two months ago orbiting TRAPPIST-1, but LHS 1140b is deemed exceptional. Jason Dittmann, an astronomer at Harvard University that lead the research group, says it's the most interesting exoplanet he has seen in the past decade. In contrast with the TRAPPIST-1 star, LHS 1140 spins slowly and does not emit much high-energy radiation, which may also help the likelihood of life on its planet.

The planet is circa 5*10^9 years old, 500*10^6 years older than Earth. The diameter is 40% larger, the mass 6.6 times that of Earth, and gravity is 3.4 times that of Earth.

The first exoplanet was discovered in 1995 and since then at least 2000 has been discovered.

Many more details are available in a research letter (pdf).

Original Submission

takyon writes:

Another study has cast doubt on the habitability of an Earth-like exoplanet in the "habitable zone" of a red dwarf, in this case Proxima Centauri specifically:

At only four light-years away, Proxima b is our closest known extra-solar neighbor. However, due to the fact that it hasn't been seen crossing in front of its host star, the exoplanet eludes the usual method for learning about its atmosphere. Instead, scientists must rely on models to understand whether the exoplanet is habitable.

One such computer model considered what would happen if Earth orbited Proxima Centauri, our nearest stellar neighbor and Proxima b's host star, at the same orbit as Proxima b. The NASA study, published on July 24, 2017, in The Astrophysical Journal Letters [DOI: 10.3847/2041-8213/aa7eca], suggests Earth's atmosphere wouldn't survive in close proximity to the violent red dwarf.

[...] In Proxima Centauri's habitable zone, Proxima b encounters bouts of extreme ultraviolet radiation hundreds of times greater than Earth does from the sun. That radiation generates enough energy to strip away not just the lightest molecules — hydrogen — but also, over time, heavier elements such as oxygen and nitrogen.

The model shows Proxima Centauri's powerful radiation drains the Earth-like atmosphere as much as 10,000 times faster than what happens at Earth.

Previously: "Earth-Like" Exoplanet Found in Habitable Zone of Proxima Centauri
Proxima b May Have Oceans
Researchers Suffocate Hopes of Life Support in Red Dwarf "Habitable Zones"
Proxima B Habitability Study Adds Climate Model

Related: MAVEN Results Find Solar Wind and Radiation Responsible for Stripping the Martian Atmosphere

Original Submission

takyon writes:

Hubble Space Telescope observations suggest that the exoplanets orbiting TRAPPIST-1 in the habitable zone could have water on their surfaces, while the planets closer to the star have likely lost any surface water they may have had:

An international team of scientists, led by Swiss astronomer Vincent Bourrier of the Observatoire de l'Université de Genève, used the [Hubble] space telescope to study the amount of ultraviolet light hitting the planets and measure the amount of hydrogen these worlds are venting into space. The results suggest the innermost planets, TRAPPIST-1b and TRAPPIST-1c, could have lost as much as 20 Earth-oceans-worth of water in the last eight billion years. The outer planets, however, including e, f, and g, which orbit in the habitable zone, would have lost less water, and could still retain vast stores of liquid water on the surface.

[...] The researchers used Hubble to measure the amount of ambient hydrogen floating around the TRAPPIST-1 planets as well as the intensity of ultraviolet light coming from the host star, an ultracool dwarf star. The amount of ultraviolet radiation coming from TRAPPIST-1 suggests the inner planets could have lost an enormous amount of water over the eons, something that is supported by the abundant hydrogen surrounding the planets—a possible indicator of water vapor. Most importantly, the radiation hitting the outer planets and the amount of hydrogen surrounding them suggests these worlds, similar to Earth in many ways, might still retain atmospheric water vapor and even liquid water on the surface.

[...] Whether or not these planets could actually support life is still an open question. First of all, the observations from Hubble are not conclusive, and further observations from other observatories as well as computer simulations are required to support or dispute the possibility of water on the TRAPPIST-1 planets.

"While our results suggest that the outer planets are the best candidates to search for water with the upcoming James Webb Space Telescope, they also highlight the need for theoretical studies and complementary observations at all wavelengths to determine the nature of the TRAPPIST-1 planets and their potential habitability," says Bourrier.

Also at Hubble News and Space.com.

Temporal Evolution of the High-Energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

Original Submission

takyon writes:

Astronomers using the High Accuracy Radial velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile have discovered an Earth-sized exoplanet orbiting a red dwarf in its "habitable zone". The star, Ross 128, is about 10.89 light years away and is less active than Proxima Centauri, possibly boosting the chances of its exoplanet being habitable. Ross 128b has a minimum mass of about 1.35 Earth masses, and is considered by its discoverers to be "the best temperate [exo]planet known to date". The next step will be to determine the atmospheric composition of Ross 128b:

There's still uncertainty about whether Ross 128 b is within its star's habitable zone, but scientists say that with temperatures of between -60 and +20°C, it can be considered temperate.

Next, astronomers want to study the atmospheric composition and chemistry of suitable, nearby worlds like Ross 128 b. The detection of gases such as oxygen could potentially point to biological processes on planets orbiting other stars.

Several gases have already been detected in the atmospheres of exoplanets, but this line of enquiry is expected to be boosted immeasurably when observatories such as the European Southern Observatory's Extremely Large Telescope (E-ELT) and Nasa's James Webb Space Telescope (JWST) come online in the next few years.

Although currently 11 light-years from Earth, the new planet's parent star Ross 128 is moving towards us and is expected to overtake Proxima Centauri as our nearest stellar neighbour in just 79,000 years - a heartbeat on cosmic timescales.

A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs (open, DOI: 10.1051/0004-6361/201731973) (DX)

Original Submission

takyon writes:

A study has found that the two outermost TRAPPIST-1 exoplanets are the most likely to be able to retain their atmospheres:

The last thing the planets around the red dwarf star TRAPPIST-1 need is abundant sunshine. Active eruptions and flares from the star would wreak havoc on the rocky planets in orbit. But fortunately, the outer planets might be safe from this barrage of high-energy space weather.

According to a new study in the Proceedings of the National Academy of the Sciences [DOI: 10.1073/pnas.1708010115] [DX], the outer planets of the system could cling on to their atmospheres. This finding is despite previous studies showing that TRAPPIST-1 might be so active that it blows away planetary atmospheres.

[...] The new results show that while all seven planets could retain their atmosphere, the more likely scenario is that the outermost two, -1g and -1h, have the best odds (and -1e and -1f have a weaker chance.)

This could be resolved by JWST observations.

Original Submission

takyon writes:

Proxima Centauri b confirmed as nearest exoworld

Four years ago, scientists made one of the most exciting exoplanet discoveries so far, a rocky planet similar in size to Earth orbiting the nearest star to the sun, Proxima Centauri. While the detection seemed solid, more confirmation is always good, and now the ESPRESSO spectrograph on the Very Large Telescope (VLT) in Chile has provided that extra and more detailed confirmation. The news was announced by the University of Geneva (UNIGE) on May 28, 2020.

[...] Proxima Centauri b is very similar in size to Earth, with a mass of 1.17 Earth masses. It orbits its star in only 11.2 days, in contrast to our Earth's year-long orbit around our sun. That means Proxima Centauri b is a lot closer to its star than Earth is to the sun. But, because the star is a red dwarf – much smaller and cooler than our sun – its orbit is indeed within the habitable zone of Proxima Centauri. Interestingly, Proxima Centauri b receives about the same amount of solar energy from its star that Earth does from our sun.

[...] The mass of Proxima b was previously estimated to be 1.3 Earth masses. The accuracy of the new measurement of 1.17 Earth masses is unprecedented, according to Michel Mayor, the "architect" of all ESPRESSO-type instruments:

ESPRESSO has made it possible to measure the mass of the planet with a precision of over one-tenth of the mass of Earth. It's completely unheard of.

The new confirmation of Proxima Centauri b is exciting, but there may be more surprises in store ... there is also possible evidence of another and smaller planet in the newest data. A secondary detection was also made, although it isn't certain whether it is actually a planet. If it is, it is even smaller than Proxima Centauri b. [...] If it is a planet, it would be more akin to Mars or Mercury in size and mass – estimated at a minimum Earth mass of 0.29 ± 0.08 – and orbits the star in only 5.15 days. It wouldn't be too surprising, though, in that low-mass stars like red dwarfs tend to have multiple planets in their systems. More observations will be required to either confirm or refute this possible second planet.

Journal Reference
Mascareño, A. Suárez, Faria, J. P., Figueira, P., et al. Revisiting Proxima with ESPRESSO, (https://arxiv.org/abs/2005.12114v1)

Proxima Centauri - Planetary system

Previously: ESO Confirms Reports of Proxima Centauri Exoplanet
Proxima b May Have Oceans
Dust Belts and Possible Additional Exoplanet Spotted Around Proxima Centauri
First Light for VLT's ESPRESSO Exoplanet Hunter
Very Large Telescope's ESPRESSO Combines Light From All Four Unit Telescopes for the First Time
Proxima Centauri's No Good, Very Bad Day
High Levels of Ultraviolet Radiation Should Not Preclude Life on Exoplanets
Icy second planet potentially spotted orbiting Proxima Centauri

Original Submission