Three times the mass of Jupiter, the first ever planet to swing around its star in a bizarre way.
Astronomers have discovered a planet three times the mass of Jupiter traveling a long, ovoid path around its star. If this planet were somehow placed in our own solar system, it would rotate from our asteroid belt to beyond Neptune.
Other giant planets with highly elliptical orbits have been found around other stars, but none of these worlds has been located in the very outer reaches of their star systems like this.
"This planet is unlike the planets in our solar system, but more than it is unlike all the other exoplanets we have found so far," says Sarah Blunt, a Caltech graduate student and the first author of a new study published in The Astronomical Journal . "Other planets found far from their stars tend to have very low eccentrics, which means their orbits are circular. The fact that this planet has so much eccentricity speaks of some difference in the way it has formed or evolved over other planets. ”
The planet was discovered using the radial velocity method, an exoplanet workhorse that discovers new worlds by tracking their parent stars 'oscillating' in response to gravitational pulls from those planets.
However, analyzes of these data usually require observations made throughout the orbital period of the planet. For planets orbiting far from their stars, this can be difficult: a full orbit can take tens or even hundreds of years.
Searching for the Planet in California, led by Caltech Professor of Astronomy Andrew W. Howard, is one of the few groups that have observed stars over the decades required to find long-lived exoplanets use of radial velocity.
The data needed to find the new planet were first provided by the WM Keck Observatory in Hawaii. In 1997, the team began using the Kirk High Resolution Spectrometer (HIRES) to make measurements of a planet star called HR 5183.
"The key was constancy," Howard said. "Our team has been following this star with the Keck Observatory for more than two decades and has only seen evidence of the planet in the last few years! Without these long-term efforts, we would never have found this planet.
In addition to the Keck Observatory, the California Planet Search also uses the Lik Observatory in Northern California and the McDonald Observatory in Texas.
Astronomers have been watching HR 5183 since the 1990s, but have no data corresponding to a complete orbit on the planet called HR 5183 b because it orbits its star approximately every 45 to 100 years. The team found the planet instead because of its strange orbit.
"This planet spends most of its time in the lever in the outer part of the planetary system of its star in this highly eccentric orbit, then it begins to accelerate and slingshot your star, "explains Howard. "We found this sling movement. We saw the planet come in and now it's on its way. This creates such a distinctive signature that we can be sure that it is a real planet, even though we have not seen a complete orbit. ”
New findings suggest that it is possible to use the radial velocity method to detect other distant planets without waiting for decades. And researchers suggest that looking for more planets like this could shed light on the role of giant planets in shaping their solar systems.
Planets are formed by disks of material left after the formation of stars. This means that the planets must go in a flat, circular orbit. For a newly discovered planet to be in such an eccentric orbit, it must have received a gravitational blow from some other object.
The most plausible scenario, according to the researchers, is that the planet once had a neighbor of similar size. When the two planets get close enough to each other, one pushes the other out of the solar system, forcing HR 5183 b into a highly eccentric orbit.
"This newly-discovered planet would essentially come in as a destructive ball," Howard says, "knocking something out of the system."
This finding shows that our understanding of planets outside our solar system is still evolving. . Researchers continue to discover worlds that are unlike anything in our solar system or the solar system we have already discovered.
"Copernicus taught us that Earth is not the center of the solar system, and as we expand into the discovery of other exoplanet solar systems, we expected them to be carbon copies of our own solar system," Howard explains, "but this is just one surprise after another in this area. This newly discovered planet is another example of a system that is not the image of our solar system, but has remarkable characteristics that make our universe incredibly rich in diversity. "
The study, entitled" Radial velocity of Jovian's eccentric orbit at 18AU, "was funded by the National Science Foundation, NASA, Tennessee State University, Tennessee Patriotic Association, Beatrice Foundation, Beatrice Foundation, for the Trotier and Caltech families. Other Caltech contributors include: BJ Fulton, IPAC Officer; former PhD student Sean Mills (BS & # 39; 12); Eric Petigura, a former doctoral student now based at UCLA; and Arpita Roy, R.A. & G.B.