Planet 'Reared' by Four Parent Stars
This artist's conception shows the 30 Ari system, which includes four stars and a planet. The planet, a gas giant, orbits its primary star (yellow) in about a year's time. Image copyright: Karen Teramura, UH IfA.
› Full image and caption
The four stars and one planet of the 30 Ari system are illustrated in
this diagram. This quadruple star system consists of two pairs of stars:
30 Ari B and 30 Ari A. Image credit: NASA/JPL-Caltech. › Full image and caption
-- Astronomers have discovered the second known case of a planet residing in a quadruple star system.
-- The planet was known before, but was thought to have only three stars, not four.
-- The findings help researchers understand how multiple star systems can influence the development and fate of planets.
Growing up as a planet with more than one parent star has its
challenges. Though the planets in our solar system circle just one star
-- our sun -- other more distant planets, called exoplanets, can be
reared in families with two or more stars. Researchers wanting to know
more about the complex influences of multiple stars on planets have come
up with two new case studies: a planet found to have three parents, and
another with four.
The discoveries were made using instruments fitted to telescopes at
the Palomar Observatory in San Diego: the Robo-AO adaptive optics
system, developed by the Inter-University Center for Astronomy and
Astrophysics in India and the California Institute of Technology in
Pasadena, and the PALM-3000 adaptive optics system, developed by NASA's
Jet Propulsion Laboratory in Pasadena, California, and Caltech.
This is only the second time a planet has been identified in a
quadruple star system. While the planet was known before, it was thought
to have only three stars, not four. The first four-star planet, KIC
4862625, was discovered in 2013 by citizen scientists using public data
from NASA's Kepler mission.
The latest discovery suggests that planets in quadruple star systems
might be less rare than once thought. In fact, recent research has shown
that this type of star system, which usually consists of two pairs of
twin stars slowly circling each other at great distances, is itself more
common than previously believed.
"About four percent of solar-type stars are in quadruple systems,
which is up from previous estimates because observational techniques are
steadily improving," said co-author Andrei Tokovinin of the Cerro
Tololo Inter-American Observatory in Chile.
The newfound four-star planetary system, called 30 Ari, is located
136 light-years away in the constellation Aries. The system's gaseous
planet is enormous, with 10 times the mass of Jupiter, and it orbits its
primary star every 335 days. The primary star has a relatively close
partner star, which the planet does not orbit. This pair, in turn, is
locked in a long-distance orbit with another pair of stars about 1,670
astronomical units away (an astronomical unit is the distance between
Earth and the sun). Astronomers think it's highly unlikely that this
planet, or any moons that might circle it, could sustain life.
Were it possible to see the skies from this world, the four parent
stars would look like one small sun and two very bright stars that would
be visible in daylight. One of those stars, if viewed with a large
enough telescope, would be revealed to be a binary system, or two stars
orbiting each other.
In recent years, dozens of planets with two or three parent stars
have been found, including those with "Tatooine" sunsets reminiscent of
the Star Wars movies. Finding planets with multiple parents isn't too
much of a surprise, considering that binary stars are more common in our
galaxy than single stars.
"Star systems come in myriad forms. There can be single stars, binary
stars, triple stars, even quintuple star systems," said Lewis Roberts
of JPL, lead author of the new findings appearing in the journal
Astronomical Journal. "It's amazing the way nature puts these things
together."
Roberts and his colleagues want to understand the effects that
multiple parent stars can have on their developing youthful planets.
Evidence suggests that stellar companions can influence the fate of
planets by changing the planets' orbits and even triggering some to grow
more massive. For example, the "hot Jupiters" -- planets around the
mass of Jupiter that whip closely around their stars in just days --
might be gently nudged closer to their primary parent star by the
gravitational hand of a stellar companion.
In the new study, the researchers describe using the automated
Robo-AO system on Palomar Observatory to scan the night skies, searching
hundreds of stars each night for signs of stellar companions. They
found two candidates hosting exoplanets: the four-star system 30 Ari,
and a triple-star planetary system called HD 2638. The findings were
confirmed using the higher-resolution PALM-3000 instrument, also at
Palomar Observatory.
The new planet with a trio of stars is a hot Jupiter that circles its
primary star tightly, completing one lap every three days. Scientists
already knew this primary star was locked in a gravitational tango with
another star, about 0.7 light-years away, or 44,000 astronomical units.
That's relatively far apart for a pair of stellar companions. The latest
discovery is of a third star in the system, which orbits the primary
star from a distance of 28 astronomical units -- close enough to have
influenced the hot Jupiter's development and final orbit.
"This result strengthens the connection between multiple star systems and massive planets," said Roberts.
In the case of Ari 30, the discovery brought the number of known
stars in the system from three to four. The fourth star lies at a
distance of 23 astronomical units from the planet. While this stellar
companion and its planet are closer to each other than those in the HD
2638 system, the newfound star does not appear to have impacted the
orbit of the planet. The exact reason for this is uncertain, so the team
is planning further observations to better understand the orbit of the
star and its complicated family dynamics.
JPL is managed for NASA by the California Institute of Technology in Pasadena.
Media Contact
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California
818-354-4673
whitney.clavin@jpl.nasa.gov
Source: JPL-Caltec/News
