About 6,500 light years away, a Jupiter-like planet orbits a dim, white dwarf star. The pair can offer astronomers insight into our own solar system’s distant future, according to research published on October 13 in the journal Nature.
The new planet, dubbed MOA-2010-BLG-477Lb, is the first Jupiter-sized planet orbiting a white dwarf star at a Jupiter-like distance, reports Ken Croswell for Science News. The discovery suggests that if a planet’s orbit is beyond the destructive range of a red giant, it can survive that violent phase and stick around after the star collapses into a much smaller, dimmer white dwarf. Although Earth probably won’t survive the self-destruction of the sun in five billion years, the finding is good news for Jupiter, Saturn and beyond.
“It would have been very easy to lose this planet,” says Juliette Becker, an astrophysicist at Caltech who was not involved in the new research, to Nadia Drake at National Geographic. “Most likely it barely avoided destruction.”
Astronomers first spotted MOA-2010-BLG-477Lb in 2010 using the Keck II telescope in Hawaii. The research team, led by University of Tasmania astrophysicist Joshua Blackman, detected the sudden brightening of a distant star. A star in the middle caused the change in appearance. During a microlensing event, its gravity bends the distant star’s light so that it becomes focused on Earth, like a magnifying glass focusing sunlight into one spot, per Science News.
Additional distortions of the distant star’s appearance revealed the presence of the Jupiter-sized planet orbiting the middle star. The researchers took more measurements in 2015, 2016 and 2018 to identify the middle star, but it proved difficult to observe.
“We expected that we’d see a star similar to the sun,” says Blackman to Science News. “And so we spent quite a few years trying to figure out why on Earth we didn’t see the star which we expected to see.”
The team ruled out the possibility of a neutron star—which is more than ten times the mass of the sun—and a black hole. Additional calculations pointed toward a white dwarf of about half the mass of the sun.
“We knew it had to be a dark star that was a bit less massive than the sun, and white dwarfs are the obvious choice,” says study co-author David Bennett, a physicist at NASA’s Goddard Space Flight Center, to National Geographic.
While many white dwarfs are surrounded by the rocky debris of planets destroyed during their red giant phase, only a few have been found with planets intact. Last year, a team found an intact Jupiter-like planet called WD 1856 b orbiting a white dwarf, reports Becky Ferreira for the New York Times. Unlike the planet described in the recent Nature study, WD 1856 b orbits very close to its star, so it may have moved closer after the star collapsed.
“If I had to guess, I would say that theirs is a much more common population because it just has to stay there and have nothing happen to it,” says Massachusetts Institute of Technology physicist Andrew Vanderburg, who led the research into WD 1856 b, to the New York Times. “That feels to me like the most likely outcome, at least at this point in the universe’s history.”
Astronomers will be able to refer to these white dwarf systems as they investigate how often planets survive their stars’ final stages. And new telescopes, like the Nancy Grace Roman Space Telescope that is expected to launch in the mid-2020s, will be able to spot more white dwarfs and their planetary companions. If exoplanets are common around white dwarf stars, then there may be even more exoplanets than current estimates suggest.
“That means that our counting of planets in the galaxy has likely been underestimated until now,” says Ohio State University astronomer Scott Gaudi to National Geographic. “In the exoplanet field, the joke is, every rock you turn over, you find a new planet.”