Chapter 21

Exoplanet

a planet orbiting a star other than our Sun

Protostar

a very young star still in the process of formation, before nuclear fusion begins

Why was the Kepler mission not able to find planets smaller than Mars, even though it was in space (and had no Earth atmosphere to deal with)?

Such planets make dips in the light of the star that are too small for Kepler to detect

The telescope that allowed astronomers to discover most of the planets found with the transit method was called

The Kepler Mission

The Orion Nebula is

a large cloud of gas and dust illuminated by the light of newly formed stars within it

Super-earth

a planet larger than Earth, generally between 1.4 and 2.8 times the size of our planet

mini-Neptune

a planet that is intermediate between the largest terrestrial planet in our solar system (Earth) and the smallest jovian planet (Neptune); generally, mini-Neptunes have sizes between 2.8 and 4 times Earth's size

Planets in the habitable zone of their stars: are so far from their stars that it is very difficult to discover them, are always the planets closest to the star, are also called hot Jupiters, cannot exist around stars that are red dwarfs (spectal type M), are at a temperature where water can exist as a liquid

are at a temperature where water can exist as a liquid

The closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun?

it would be significantly closer to Proxima Centauri than ours is to the Sun

When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall?

its mass

giant molecular clouds

large, cold interstellar clouds with diameters of dozens of light-years and typical masses of 10^5 solar masses; found in the spiral arms of galaxies, these clouds are where stars form

Herbig-Haro (HH) object

luminous knots of gas in an area of star formation that are set to glow by jets of material from a protostar

What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?

measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star

The big surprise about the first planet discovered around another regular star was that it

orbited so close to its star it took only 4 days to go around

What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?

the disks show lanes that are empty of dust within them

stellar wind

the outflow of gas, sometimes at speeds as high as hundreds of kilometers per second, from a star

A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?

to the left

transit

when one astronomical object moves in front of another