Rocky Planet Found Around 10 Billion-Year-Old Star


This artist’s rendition shows TOI-561, one of the oldest, most metal-poor stars known in the Milky Way Galaxy. This star hosts a hot, rocky exoplanet (center) as well as two gas planets (to the left).
W. M. Keck Observatory / Adam Makarenko

Astronomers have discovered three planets orbiting a star about 10 billion years old — one of them rocky. The star, TOI 561 (meaning it was the 561st object of interest from the Transiting Exoplanet Survey Satellite), is in our galaxy’s older thick disk, which means its planets have a nice view from on high of the Milky Way’s spiral.

The star has three planets, with diameters 1.5, 3, and 2 times Earth’s. The innermost one is rocky, with three times Earth’s mass, but on a period of 0.44 days, it’s anything but Earth-like. Its dayside surface temperature is around 2500K (4,000°F). That’s almost twice as hot as Earth’s magma, and it’s surely molten. What it actually looks like is uncertain, because as lead scientist Lauren Weiss (University of Hawaii, Manoa) notes, “It exceed temperatures where geophysicists have made lava in the lab.”

Thick Disk of the Milky Way
Illustration showing the structural components of the Milky Way galaxy. The star TOI 561 is located in the thick disk (marked in red-orange), which contains a sparse, older population of stars.
Kaley Brauer / MIT

Astronomers have found planets around old stars before, and even around chemically poor stars that lack many heavier elements. Yet the mere fact that this planet came to be is of interest to astronomers. “We now have evidence that the universe has been forming rocky planets for the last 10 billion years, more than double the age of our own solar system, and nearly since the origin of the universe itself,” Weiss says.

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