### Taking a Bite Out of an Asteroid

#### TL;DR

1. Taking a bite out of an asteroid
2. A huge goof by Star Wars
3. 7 exoplanets!

#### Current events

Last night Japanese spacecraft Hayabusa-2 grabbed a rock sample from the asteroid Ryugu, which it has been orbiting since June after a 3.5 year journey. Hayabusa-2 already deployed two tiny rovers to the asteroid surface in September, and these rovers are super cool because they don’t actually roll on the surface the way we might expect, since the gravity on the asteroid is way too low. Instead, they bounce around like grasshoppers, using a torque generated by internal rotating masses. Hayabusa-2 collected the sample by approaching the surface with a sampling horn, firing a 5-gram tantalum bullet into the rock, and collecting the ejected materials into a catcher. After three samples, the probe is scheduled to depart Ryugu in December 2019 and return the samples to Earth December 2020.

 Artist's impression of Hayabusa-2 collecting a sample from Ryugu

#### Today I learned

In addition to a lightyear, there are two other metrics of distance commonly used for space. One is called the Astronomical Unit (AU), which is simply the average distance from the Earth to the Sun, about 93mm miles. The other is the parsec, which is visualized in the diagram below. Given a right triangle where the shorter leg is 1 AU and the opposite angle is 1 arcsecond (1/3600 of a degree), the other leg (the green line) is equal to one parsec. As it turns out, one parsec =  19 trillion miles.
There's a ridiculous scene from Star Wars where Han Solo says he piloted the Millennium Falcon through the Kessel Run in less than 12 parsecs. Now that you're all informed, you understand why this phrase makes absolutely no sense. Parsecs are a measure of distance, not time (see the video below, the phrase starts at 0:10)

#### This day in space history

On February 22, 2017, NASA announced the discovery of 7 exoplanets orbiting a small, cool star called TRAPPIST-1 nearby (only 40 lightyears!). 3 of the exoplanets orbit within the habitable zone, meaning they orbit in a range that might allow temperatures that would sustain liquid water and potentially life. This is the most Earth-size planets ever discovered in the habitable zone of a single star.

 Artist's impression of the TRAPPIST-1 system

Of these three, planet TRAPPIST-1e is the most similar to Earth, with about the same mass, radius, gravity, and temperature, scoring very high on the Earth Similarity Index. The exoplanets were discovered by the Spitzer Space Telescope using the transit method and will be a key priority for further study for the upcoming new James Webb Space Telescope.