Astronomers have discovered TOI-561b, a rocky super-Earth orbiting one of the Milky Way's oldest stars. Its extreme heat, however, makes life there virtually impossible.
To unravel planetary formation and evolution, scientists study worlds spanning cosmic timescales—from fledgling systems to ancient relics. Exoplanet surveys have fueled major breakthroughs in recent years.
Just months ago, the Very Large Telescope (VLT) in Chile imaged a newborn planetary system 520 light-years away. Now, NASA's TESS mission and the WM Keck Observatory in Hawaii have revealed a planet at the other extreme.
TOI-561b resides about 280 light-years away. This rocky super-Earth is 50% larger and three times more massive than Earth. Strikingly, its Earth-like density points to an incredibly ancient origin.
Heavy elements like iron and magnesium arise from fusion in massive stars' cores, building up over eons through supernova blasts. TOI-561b's lower heavy-element content implies it formed about 10 billion years ago.
This aligns with its host star in the galaxy's thick disk—a haven for ancient, metal-poor stars. Simply put, TOI-561b ranks among the oldest rocky exoplanets known, circling one of our galaxy's eldest stars. "Its existence shows that the Universe formed rocky planets very early in its history," says lead author Lauren Weiss of the University of Hawaii.
TOI-561b hugs its star tightly, orbiting every 12 hours—a "year" there equals half an Earth day. Its surface averages over 1726 degrees Celsius, rendering it far too hot for life as we know it, according to collaborators at the University of California, Riverside.
The system hosts two more planets, but they are oversized and low-density gas giants, like Jupiter or Saturn. Details appear in The Astronomical Journal.
