Astro 9 Flashcards
What is an exoplanet?
A planet that orbits a star other than the Sun; also called an “extrasolar planet”.
As of April 2025, how many confirmed exoplanets and candidates are there?
$$ 5867 $$ confirmed exoplanets and $$ 7760 $$ candidate exoplanets.
Which types of main sequence stars are most likely to support planets with life?
G, K, and M stars (which make up 97–99% of main sequence stars).
Why don’t O and B stars typically support life-bearing planets?
Their lifespans are too short for complex life to develop.
Can planets exist in binary or multiple star systems?
Yes, detections and simulations show planets can form, though some orbits are excluded.
Is the Solar System typical compared to other planetary systems?
No, exoplanet systems are much more varied in orbits, masses, and planet types.
What are “Super-Earths”?
Planets with masses between Earth and Neptune, common in the galaxy but not found in our Solar System.
What is the most common type of planet discovered by Kepler?
“Super-Earths”, which do not exist in our Solar System.
How do most exoplanet orbits compare to those in our Solar System?
Many exoplanets have more eccentric orbits than those in our Solar System.
Why are observational biases important in exoplanet studies?
Because detection methods are more sensitive to large or close-in planets, which can skew our understanding of the true distribution.
What equation helps account for selection effects in planet detection?
$$ \text{Number seen} = (\text{True number}) \times (\text{Chance to see}) $$.
How common are planets around stars?
There is an average of about $$ 1 $$ planet per star; at least 54% of stars have planets.
What fraction of stars have potentially habitable planets?
About 20% of stars.
What are “Hot Jupiters”?
Massive, gaseous planets orbiting very close to their star, often with tilted orbits and high temperatures.
Does the classic “dust accretes to planetesimals to planets” nebular model explain all exoplanet systems?
No; it needs modification to explain phenomena like elliptical orbits, Super-Earths, and Hot Jupiters.
What stellar property is linked to higher planet occurrence rates?
Higher metallicity (often measured by $[\mathrm{Fe}/\mathrm{H}]$).
How far away are some potentially Earth-like planets?
A handful are within 30 light-years; many are within a few hundred light-years.
Why is understanding observational bias crucial in exoplanet science?
To correctly infer the “true” population of planets, not just those easiest to detect.
Describe the diversity of exoplanets found so far.
There is much more diversity in orbits, masses, and sizes than the Solar System suggests; many rules based on our system break down.
What type of orbits are better for life?
More circular orbits, since they provide stability of location and temperature.
What stellar classes are defined in the context of exoplanets?
G, F, K, and M stars.
