The 365 Days of Astronomy Astronomy Cast Ep. 34: Discovering Another Earth
Nov 3, 2025
Astronomers have discovered an Earth-sized planet orbiting Gliese 581, raising exciting questions about habitability. The discussion dives into the methods used, such as radial velocity for measuring planet characteristics. Insights on temperature conditions suggest the potential for liquid water. The hosts explore what future observations are possible, the challenges of detecting distant atmospheres, and the significance of finding true Earth analogs. Also highlighted are ongoing missions and the tug-of-war between funding for robotic science and human spaceflight.
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Red Dwarfs Amplify Small-Planet Signals
- Red dwarf stars like Gliese 581 are low-mass and faint, making small planets easier to detect by their gravitational tug.
- HARPS in Chile detects tiny radial-velocity shifts, enabling discovery of multiple low-mass planets around such stars.
HARPS Reaches Meter-Per-Second Precision
- HARPS measures Doppler shifts down to about one meter per second, revealing planets that induce very small stellar motions.
- This precision lets astronomers find planets with masses only a few times Earth's mass by tracking stellar radial velocities.
A Dense, Close-In Yet Temperate World
- The newly reported planet has a minimum mass of about 5.6 Earth masses and an estimated radius ~1.5 Earth radii.
- Its short 13-day orbit at ~0.07 AU still yields temperate conditions because Gliese 581 is very faint.
