Astronomers have discovered two potentially habitable worlds orbiting a red dwarf star in our cosmic backyard. The extra-solar planets or "exoplanets" are located just 16 light-years away and have masses similar to that of our planet.
They are located in the 'habitable zone', or 'Goldilocks zone' of their star, GJ 1002, defined as the shell around a star that is neither too hot nor too cold to support liquid water, a vital ingredient for life.
"Nature seems bent on showing us that Earth-like planets are very common," study author Alejandro Suárez Mascareño of the Instituto de Astrofisica de Canarias (IAC) said in a statement. "With these two we now know seven in planetary systems quite near to the sun."
Related: Astronomers discover strange twin alien planets might be water worlds
Because liquid water is essential for life to exist, planets in habitable zones are the focus of our search for life elsewhere in the universe, though just being in a habitable zone is no guarantee of being able to support life. For example, in the solar system both Venus and Mars are in the sun's habitable zone yet neither could currently support life.
Because GJ 1002 is a relatively cool red dwarf, its habitable zone — and these two new exoplanets — are much closer to it than Earth is to the sun. The innermost planet, designated GJ 1002b, takes just around 10 days to orbit the star while the outer planet, GJ 1002c, completes an orbit in 21 days.
"GJ 1002 is a red dwarf star, with barely one-eighth the mass of the sun," study co-author and IAC researcher, Vera María Passegger, said in the statement. "It is quite a cool, faint star. This means that its habitability zone is very close to the star."
The proximity of both planets to Earth means that they could be excellent targets for astronomers aiming to study the atmospheres of Earth-like worlds outside the solar system.
The exoplanets were discovered as the result of a collaboration between the European Southern Observatory (ESO) instrument ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations) installed at the Very Large Telescope (VLT) in the Atacama desert region of Northern Chile, and CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs) at the Calar Alto Observatory in Andalucía, Southern Spain.
The two instruments observed the planets' parent star during two separate periods, CARMENES studied GJ 1002 between 2017 and 2019, while ESPRESSO collected data from the red dwarf between 2019 and 2021.
CARMENES' sensitivity over a wide range of near-infrared wavelengths makes it well-suited to detecting variations in the velocities of stars that can indicate orbiting planets.
"Because of its low temperature the visible light from GJ 1002 is too faint to measure its variations in velocity with the majority of spectrographs" a researcher at the Institute of Space Sciences (ICE-CSIC), Ignasi Ribas, explained.
While ESPRESSO and the light-gathering power of the VLT allowed astronomers to make observations of the system that wouldn't have been possible with any other Earth-based telescope, it was the combination of these two powerful instruments that delivered results which in isolation would have struggled to achieve and lead to the discovery of these exoplanets.
"Either of the two groups would have had many difficulties if they had tackled this work independently," concluded Suárez Mascareño. "Jointly we have been able to get much further than we would have done acting independently."
The astronomers now hope to use the ANDES spectrograph on the Extremely Large Telescope under construction in the atmosphere of GJ 1002c.
The team's research is published in the journal Astronomy & Astrophysics.
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Interesting. I read another report on this system. Astronomers discover two potentially habitable exo-Earths around a star near the sun, https://phys.org/news/2022-12-astronomers-potentially-habitable-exo-earths-star.html
"An international scientific team led by researchers at the Instituto de Astrofísica de Canarias (IAC) has discovered the presence of two planets with Earth-like masses in orbit around the star GJ 1002, a red dwarf not far from the solar system. Both planets are in the habitability zone of the star. "Nature seems bent on showing us that Earth-like planets are very common. With these two we now know 7 in planetary systems quite near to the sun," explains Alejandro Suárez Mascareño, an IAC researcher, who is the first author of the study accepted for publication in Astronomy & Astrophysics...The newly discovered planets orbit the star GJ 1002, which is at a distance of less than 16 light years from the solar system. Both of them have masses similar to that of the Earth, and they are in the habitability zone of their star. GJ 1002b, the inner of the two, takes little more than 10 days to complete an orbit around the star, while GJ 1002c needs a little over 21 days. "GJ 1002 is a red dwarf star, with barely one eighth the mass of the sun. It is quite a cool, faint star. This means that its habitability zone is very close to the star," explains Vera María Passegger, a co-author of the article and an IAC researcher. The proximity of the star to our solar system implies that the two planets, especially GJ 1002c, are excellent candidates for the characterization of their atmospheres based either on their reflected light, or on their thermal emission…"
I did not see anything that claimed these were water worlds, perhaps I missed this. GJ 1002 may not be said to be a water world but habitable with possible liquid water on the exoplanets. Not much is definitely known about these two exoplanets, or even if they have atmospheres.
ref - Two temperate Earth-mass planets orbiting the nearby star GJ 1002, https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/202244991, 21-Nov-2022.
My notes. The NASA ADS Abstract, Two temperate Earth-mass planets orbiting the nearby star GJ1002, https://ui.adsabs.harvard.edu/abs/2022arXiv221207332S/abstract, December 2022.
"We report the discovery and characterisation of two Earth-mass planets orbiting in the habitable zone of the nearby M-dwarf GJ~1002 based on the analysis of the radial-velocity (RV) time series from the ESPRESSO and CARMENES spectrographs. The host star is the quiet M5.5~V star GJ~1002 (relatively faint in the optical, V∼13.8 mag, but brighter in the infrared, J∼8.3 mag), located at 4.84 pc from the Sun. We analyse 139 spectroscopic observations taken between 2017 and 2021. We performed a joint analysis of the time series of the RV and full-width half maximum (FWHM) of the cross-correlation function (CCF) to model the planetary and stellar signals present in the data, applying Gaussian process regression to deal with the stellar activity. We detect the signal of two planets orbiting GJ~1002. GJ~1002~b is a planet with a minimum mass mpsini of 1.08 ± 0.13 M ⊕ with an orbital period of 10.3465 ± 0.0027 days at a distance of 0.0457 ± 0.0013 au from its parent star, receiving an estimated stellar flux of 0.67 F⊕ . GJ~1002 c is a planet with a minimum mass mpsini of 1.36 ± 0.17 M ⊕ with an orbital period of 20.202 ± 0.013 days at a distance of 0.0738 ± 0.0021 au from its parent star, receiving an estimated stellar flux of 0.257 F⊕ . We also detect the rotation signature of the star, with a period of 126 ± 15 days. GJ~1002 is one of the few known nearby systems with planets that could potentially host habitable environments. The closeness of the host star to the Sun makes the angular sizes of the orbits of both planets ( ∼ 9.7 mas and ∼ 15.7 mas, respectively) large enough for their atmosphere to be studied via high-contrast high-resolution spectroscopy with instruments such as the future spectrograph ANDES for the ELT or the LIFE mission."
My note. Both b and c are list at the exoplanet.eu site. http://exoplanet.eu/catalog/gj_1002_b/ No atmosphere is reported for these two explanets said to be in their host star HZ. http://research.iac.es/proyecto/exoatmospheres/index.php.
My note, GJ 1002 b is said to be about 1.08 earth masses. If radius 1.1 earth radii, mean density ~ 4.46 g cm^-3. Using a = 0.0457, GJ 1002 b = 3.4E-3 Mjup or 1.08 earth masses, e = 0, and host star mass = 0.125 Msun, I calculate P = 1.0093E+01 days or 10.0093 day orbital period. The published value = 10.3465 day. Nothing much seems known about them. They are likely two exoplanets in the HZ of the red dwarf host. This site does not confirm an atmosphere for these two exoplanets. Exoplanet atmospheres (iac.es)
Astrobiology studies are now looking at more than the HZ around a star, now the abiogenesis zone should be incorporated too.