親子觀星會

https://www.universetoday.com/147135/astronomers-are-starting-to-find-planets-in-much-longer-orbits-cooler-more-habitable-planets/

The team of astronomers published their results in a research letter titled “NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event.” Lead author is Dr Samuel Gill from the Department of Physics at the University of Warwick. The letter is published in The Astrophysical Journal Letters.

Every method of detection has an inherent selection bias. A single transit in front of a star is not enough to be considered a planet detection. At least two transits are needed. So with the transit method, detection is biased towards planets with short orbital periods. It’s also biased towards finding larger planets, which block more starlight causing a bigger dip in brightness.

In their letter, the authors write, “… the transit geometry imposes a strong selection bias for close-in orbits, and only a handful of well-characterized transiting exoplanets are known to have orbital periods longer than about 30 days.”

Since TESS only looks at most sections of the sky for 27 days, it’s biased toward detecting planets that complete two transits in that time period, meaning it’s likely to find planets close to their stars. And those planets are bound to be hot ones; too hot for liquid water or for life.
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