Stories submitted via Arthur T Knackerbracket and by NotSanguine about the exoplanet K2-18 b:
James Webb Telescope Detects Further Proof That Distant Exoplanet May Host Life
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Scientists have discovered methane and carbon dioxide in the atmosphere of K2-18 b, a distant exoplanet that has long piqued the curiosity of astronomers for having the potential to sustain life.
Using data from the James Webb Space Telescope, scientists based at NASA, the Canadian Space Agency and the European Space Agency (ESA) were able to detect the presence of carbon-bearing molecules including methane and carbon dioxide in the atmosphere of the planet that is about 8.6 times the Earth’s mass.
The discovery adds to recent studies that suggested the K2-18 b could be what is known as a Hycean exoplanet – one that has the potential to have a hydrogen-rich atmosphere and a water ocean-covered surface.
[...] “Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,” explained Prof Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper announcing these results, which will be published in The Astrophysical Journal Letters.
“Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations.”
These initial Webb observations also provided a possible detection of a molecule called dimethyl sulphide, which on Earth is only produced by life – largely emitted by the vast swathes of phytoplankton that inhabit our oceans.
“Upcoming Webb observations should be able to confirm if [dimethyl sulphide] is indeed present in the atmosphere of K2-18 b at significant levels,” added Madhusudhan.
Even though K2-18 b hosts carbon-bearing molecules and lies in the habitable zone based on the distance from its star, this does not mean it can necessarily support life. Scientists said that the planet’s large size means that its interior likely contains a large mantle of high-pressure ice.
And while Hycean worlds are predicted to have oceans of water, it is possible that the ocean is too hot to be habitable or be liquid.
Paper preprint [PDF]
Webb Discovers Methane, Carbon Dioxide in Atmosphere of K2-18 b
NASA announced that the James Webb Space Telescope (JWST) has detected carbon-based molecules (methane, carbon dioxide and other organics) in the atmosphere of an exoplanet ~120 light years from Earth.
From the NASA announcement:
A new investigation with NASA's James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. Webb's discovery adds to recent studies suggesting that K2-18 b could be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface.
The first insight into the atmospheric properties of this habitable-zone exoplanet came from observations with NASA's Hubble Space Telescope, which prompted further studies that have since changed our understanding of the system.
K2-18 b orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth in the constellation Leo. Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our solar system. This lack of equivalent nearby planets means that these 'sub-Neptunes' are poorly understood, and the nature of their atmospheres is a matter of active debate among astronomers.
The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere in K2-18 b. These initial Webb observations also provided a possible detection of a molecule called dimethyl sulfide (DMS). On Earth, this is only produced by life. The bulk of the DMS in Earth's atmosphere is emitted from phytoplankton in marine environments.
The inference of DMS is less robust and requires further validation. "Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels," explained Madhusudhan.
While K2-18 b lies in the habitable zone, and is now known to harbor carbon-bearing molecules, this does not necessarily mean that the planet can support life. The planet's large size — with a radius 2.6 times the radius of Earth — means that the planet's interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. Hycean worlds are predicted to have oceans of water. However, it is also possible that the ocean is too hot to be habitable or be liquid.
"Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy," explained team member Subhajit Sarkar of Cardiff University. "We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere."
Characterizing the atmospheres of exoplanets like K2-18 b — meaning identifying their gases and physical conditions — is a very active area in astronomy. However, these planets are outshone — literally — by the glare of their much larger parent stars, which makes exploring exoplanet atmospheres particularly challenging.
The team sidestepped this challenge by analyzing light from K2-18 b's parent star as it passed through the exoplanet's atmosphere. K2-18 b is a transiting exoplanet, meaning that we can detect a drop in brightness as it passes across the face of its host star. This is how the exoplanet was first discovered in 2015 with NASA's K2 mission. This means that during transits a tiny fraction of starlight will pass through the exoplanet's atmosphere before reaching telescopes like Webb. The starlight's passage through the exoplanet atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet's atmosphere.
"This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits," said Madhusudhan. "For comparison, one transit observation with Webb provided comparable precision to eight observations with Hubble conducted over a few years and in a relatively narrow wavelength range."
"These results are the product of just two observations of K2-18 b, with many more on the way," explained team member Savvas Constantinou of the University of Cambridge. "This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets."
How Astronomers Detected Water on a Potentially Habitable Exoplanet for the First Time
Water Detected on Super Earth Exoplanet in Habitable Zone
Second "Super-Earth" Found Orbiting K2-18, 111 Light Years Away
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When astronomers were trying to determine the mass of a "super-Earth" exoplanet orbiting the red dwarf K2-18, they found a second one:
When K2-18b was first discovered in 2015, it was found to be orbiting within the star's habitable zone (aka. "Goldilocks Zone"). The team responsible for the discovery also determined that given its distance from its star, K2-18b's surface received similar amounts of radiation as Earth. However, the initial estimates of the planet's size left astronomers uncertain as to whether the planet was a Super-Earth or a mini-Neptune.
For this reason, Cloutier and his team sought to characterize the planet's mass, a necessary step towards determining it's atmospheric properties and bulk composition. To this end, they obtained radial velocity measurements of K2-18 using the HARPS spectrograph. These measurements allowed them to place mass constraints on previously-discovered exoplanet, but also revealed something extra.
[...] Essentially, their radial velocity measurements revealed that K2-18b has a mass of about 8.0 ± 1.9 Earth masses and a bulk density of 3.3 ± 1.2 g/cm³. This is consistent with a terrestrial (aka. rocky) planet with a significant gaseous [envelope] and a water mass fraction that is equal to or less than 50%. In other words, it is either a Super-Earth with a small gaseous atmosphere (like Earths) or "water world" with a thick layer of ice on top.
They also found evidence for a second "warm" Super Earth named K2-18c, which has a mass of 7.5 ± 1.3 Earth masses, an orbital period of 9 days, and a semi-major axis roughly 2.4 times smaller than K2-18b. After re-examining the original light curves obtained from K2-18, they concluded that K2-18c was not detected because it has an orbit that does not lie on the same plane.
K2-18b was discovered by the Kepler Space Observatory in 2015.
Also at the University of Toronto Scarborough.
For the first time, water has been detected on an exoplanet orbiting in its star's habitable zone.
A new study by Professor Björn Benneke of the Institute for Research on Exoplanets at the Université de Montréal, his doctoral student Caroline Piaulet and several of their collaborators reports the detection of water vapour and perhaps even liquid water clouds in the atmosphere of the planet K2-18b.
The planet is nine times the mass of Earth and circling more closely to its smaller M3 dwarf star with, a year length of only 33 days. K2-18b "receives virtually the same amount of total radiation from its host star" as Earth.
Scientists currently believe that the thick gaseous envelope of K2-18b likely prevents life as we know it from existing on the planet's surface.
Still, according to Professor Benneke "This represents the biggest step yet taken towards our ultimate goal of finding life on other planets, of proving that we are not alone."
Björn Benneke, Ian Wong, Caroline Piaulet, Heather A. Knutson, Ian J.M. Crossfield, Joshua Lothringer, Caroline V. Morley, Peter Gao, Thomas P. Greene, Courtney Dressing, Diana Dragomir, Andrew W. Howard, Peter R. McCullough, Eliza M.-R. Kempton Jonathan J. Fortney, Jonathan Fraine. Water Vapor on the Habitable-Zone Exoplanet K2-18b. Astronomical Journal (submitted), 2019 [link]
Submitted via IRC for SoyCow2718
K2-18 b was discovered in 2015 and is one of hundreds of "super-Earths"—planets with a mass between Earth and Neptune—found by NASA's Kepler spacecraft. It is a planet with eight times the mass of the Earth that orbits a so called "red dwarf" star, which is much cooler than the sun.
However, K2-18b is located in the "habitable zone" of its star which means it has the right temperature to support liquid water. Given its mass and radius, K2-18 b is not a gaseous planet, but has a high probability of having a rocky surface.
We developed algorithms to analyze the starlight filtered by this planet using transit spectroscopy, with data provided by the Hubble Space Telescope.
This enabled us to make the first successful detection of an atmosphere with water vapor around a non-gaseous planet, which is also located within the habitable zone of its star.
In order for an exoplanet to be defined as habitable, there is a long list of requirements that need to be satisfied. One is that the planet needs to be in the habitable zone where water can exist in liquid form. It is also necessary that the planet has an atmosphere to protect the planet from any harmful radiation coming from its host star.
Another important element is the presence of water, vital for life as we know it. Although there are many other criteria for habitability, such as the presence of oxygen in the atmosphere, our research has made K2-18b the best candidate to date. It is the only exoplanet to fulfil three requirements for habitability: the right temperatures, an atmosphere and the presence of water.
However, we cannot say, with current data, exactly how likely the planet is to support life. Our data are limited to an area of the spectrum—this shows how light is broken down by wavelength—where water dominates, so other molecules can unfortunately not be confirmed.