In the study, published in the The Astrophysical Journal, Radek Poleski and his team from Ohio State University identified the alien world orbiting a star in a binary system some 25,000 light-years away in the direction of Sagittarius. The binary system is composed of a star approximately two-thirds the mass of our sun, whereas its stellar partner is only one-sixth of a solar mass. The ‘exo-Uranus’ orbits the larger star.
However, at first glance, this new world seems anything but Uranus-like (or, indeed, Neptune-like), it’s actually four times more massive than the planet that we know and love. But the key here is that it has a Uranus-like orbit, a characteristic that could make it the first exoplanet to possess a Uranus-like composition — though this cannot be tested as the world is too distant for us to study its chemical makeup.
Both Uranus and Neptune are distinct from the other two gas giants in our solar system (Jupiter and Saturn) in that their thick atmospheres are loaded with methane ices; a factor that gives these two planets their blueish hue. Located further away from the sun, it seems that their orbital distance has allowed Uranus and Neptune’s icy evolution.
“Nobody knows for sure why Uranus and Neptune are located on the outskirts of our solar system, when our models suggest that they should have formed closer to the sun,” said Andrew Gould, also of Ohio State and co-investigator. “One idea is that they did form much closer, but were jostled around by Jupiter and Saturn and knocked farther out.”
This distant exo-Uranus was discovered when the world orbited in front of its star. In doing so, the world’s gravitational field, which warps space-time, created a ‘microlens’ event where the star’s light became focused and brightened from Earth’s perspective.
Microlensing events happen purely by chance and can happen anywhere in the galaxy, so we have networks of observatories around the globe that are constantly surveying the whole sky in the hope of spotting these transient brightenings. In this case, the 1.3-meter Warsaw Telescope at Las Campanas Observatory in Chile of the international Optical Gravitational Lensing Experiment (OGLE) identified two separate microlensing events — one in 2008 that revealed the presence of the main star and hinted at the presence of a planet, and a second event in 2010 that confirmed the planet and the presence of a smaller binary partner.
By combining the two microlensing observations, the team was able to measure the two stars’ masses and derive the exoplanet’s mass and orbital distance.
Interestingly, it’s the presence of the smaller binary partner that may help explain the origin of this exo-Uranus and, in turn, may also offer clues as to how our Uranus and Neptune came to migrate to the far-flung orbits they occupy today.
“Maybe the existence of this Uranus-like planet is connected to interference from the second star,” said Gould. “Maybe you need some kind of jostling to make planets like Uranus and Neptune.”
Read more at Discovery News
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