Madrid. Two new Earth-mass planets have been discovered orbiting a red dwarf star only 16 light-years away, that is, very close in astronomical terms.
The planets, GJ 1002 b and c, are in the star’s habitable zone, the orbital distance that could allow liquid water to form on a planet’s surface if it has the right kind of atmosphere, NASA reports.
The probability that red dwarf stars host habitable worlds is the subject of scientific debate. On the downside, these stars—smaller and cooler, but much longer-lived than stars like our Sun—tend to blow up frequently in their youth.
These flares could dislodge the atmospheres of nearby orbiting planets, and the two planets orbiting GJ 1002 are very close. Planet b, with a mass slightly greater than that of Earth, is the closer of the two. Its year, once around the star, lasts only 10 days. Planet c, about a third more massive than Earth, takes about 20 days to orbit the star.
On the bright side, however, GJ 1002 appears to be mature and calm enough. It is even possible that their past activity helped to accumulate a variety of molecules on the planets’ surfaces that could be used later, during the star’s quiet period, by any developing life forms that might be present.
An international team led by Alejandro Suárez Mascareño, from the University of La Laguna, discovered the two new planets using radial velocity measurements, that is, detecting the “wobbles” of the parent star caused by the gravitational tugs of the orbiting planets.
When planets move toward the far side of the star, they move the star away from us, causing the star’s light to shift toward the red end of the spectrum. When the planets move toward the near side of the star, they pull it in our direction, shifting its light toward blue.
The planetary jerks in GJ 1002 are tiny, about 1.3 meters per second, which is equivalent to moving at about 4.8 kilometers per hour. These small movements are difficult to detect.
The radial velocity method, which also reveals the mass of planets, has confirmed more than 1,000 exoplanet detections. However, most detections have been made using the “transit” method, which consists of observing a small dimming of starlight when a planet crosses in front of its star, with almost 4,000 confirmed detections.
To make their radial velocity measurements, the scientific team relied on instruments called spectrographs, which measure variations in light.
The spectrographs used to discover GJ 1002 b and c were part of two collaborative observing programs: The Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), and the high-resolution search at Calar Alto for M dwarfs with Exo-Earths with optical Échelle spectrographs. and near infrared (CARMENES).
The new planets join about 10 others in a rather exclusive category: small worlds in the “conservative” habitable zone that are less than 1.5 times the size of Earth or less than five times its mass. If we loosen the membership criteria a bit – slightly larger planets in the “optimistic” habitable zone – the group expands to about 40 exoplanets, or planets beyond our solar system.
The conservative habitable zone is a tighter limit to the region around a star that could allow planets to harbor water; optimistic habitable zones stretch that limit a bit. Any habitable zone estimate is an approximation. At the moment, the atmosphere of none of these worlds has been analyzed, and many may lack it.
A paper on the discovery has been accepted for publication in the journal Astronomy & Astrophysics.
#Scientists #find #planets #water