Wolf 503b, an exoplanet twice the size of the earth, was discovered by an international team of Canadian, American and German researchers using the Kepler Space Telescope from NASA. The find is described in a new study of which the lead author is Merrin Peterson, an Institute for Exoplanet Research (iREx), a graduate student who started her master's degree at the Université de Montreal (UdeM) in May.
Wolf 503b is about 145 light-years from Earth in the constellation Virgo; it circles every six days around its star and is therefore very close, about 10 times closer than Mercury to the sun.
"The discovery and confirmation of this new exoplanet was very fast, thanks to the collaboration that I and my advisor, Bjorn Benneke, are part of," said Peterson. "In May, when the latest version of the Kepler K2 data came in, we quickly ran a program that enabled us to find as many interesting candidate exoplanets as possible." Wolf 503b was one of them. "
The program used by the team identifies different, periodic drops that appear in the light curve of a star when a planet passes through it. In order to better characterize the system that characterizes Wolf 503b, the astronomers first obtained a spectrum of the host at the NASA Infrared Telescope Facility.
This confirmed that the star is an old & # 39; orange dwarf & # 39; is, slightly less luminous than the sun but about twice as old, and allowed a precise determination of the radius of both the star and its companion.
To confirm that the companion was indeed a planet and to prevent false-positive identification, the team obtained adaptive optics measurements from the Palomar Observatory and also examined archive data. With this they could confirm that there were no double stars in the background and that the star had no other, more massive companion that could be interpreted as a passing planet.
Wolf 503b is interesting, first because of the size. Thanks to the Kepler telescope, we know that most of the planets in the Milky Way that circle close to their stars are about the same size as Wolf 503b, somewhere between the size of the earth and Neptune (which is four times larger than Earth). Because in our solar system there is nothing like them, astronomers wonder if these planets are small and rocky & # 39; super terrestrial & # 39; or gaseous mini versions of Neptune.
A recent discovery also shows that there are considerably fewer planets that are 1.5 to 2 times as large as those of the earth, or smaller or larger than that. This drop, called the Fulton gap, could be what distinguishes the two types of planets, say researchers in their research on the discovery, published in 2017.
"Wolf 503b is one of the few planets with a radius near the opening that has a star that is clear enough to be susceptible to a more detailed study that better limits its true nature," explains Bjorn Benneke, UDEM professor and member of iREx and CRAQ.
"It provides an important opportunity to better understand the origins of this radius gap, as well as the nature of the intriguing populations of" super-earths & # 39; and "sub-Neptunes" as a whole. "
The second reason for interest in the Wolf 503b system is that the star is relatively close to the earth and is therefore very clear. One of the possible follow-up studies for bright stars is the measurement of their radial speed to determine the mass of the planets in orbit around them. A more massive planet will have a greater gravitational influence on its star and the variation in line of sight of the star over time will be greater.
The mass, together with the radius determined by the observations of Kepler, gives the bulk density of the planet, which in turn tells us something about its composition. For example, if the planet has about the same composition as the Earth in its radius, it would be about 14 times as large as the mass. If, like Neptune, it has an atmosphere rich in gas or volatile substances, it would be about half as massive.
Because of its clarity, Wolf 503 will also be an important target for the upcoming James Webb Space Telescope. Using a technique called transit spectroscopy, it will be possible to study the chemical content of the planet's atmosphere and detect the presence of molecules such as hydrogen and water. This is crucial to verify that it is similar to that of the Earth, Neptune, or is completely different from the atmosphere of planets in our solar system.
Similar observations can not be made of most planets found by Kepler, because their host stars are usually much weaker. As a result, the bulk densities and atmospheric compositions of most exoplanets are still unknown.
"By examining the nature of Wolf 503b, we will understand more about the structure of planets near the radius gap and more generally the diversity of exoplanets present in our galaxy," Peterson said. "I am looking forward to learning more about it."
Research report: "A 2 Earth Radius Planet Orbiting the Bright Nearby K-Dwarf Wolf 503," Merrin S. Peterson et al., 2018, appearing in the Astronomical Journal
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