What does guessing the number of jelly beans in a jar have to do with political polls and counting asteroids? They all have something in common: all three use statistical samples to predict a result. In other words, without having to ask every single person in the country how they’ll vote, it’s possible to pick a group of people who we think are likely to be a good representation of everyone and just ask them how they’re going to vote. From this representative sample, we can predict what everyone else will do.
Similarly, we don’t have to count every single jelly bean in the jar to get a good estimate of how many there are. Instead, we can figure out about how big each bean is, and roughly how big the jar is, and from there, we can make a pretty solid guess about how many beans the jar holds.
When it comes to asteroids, those bits of rock, ice, and dust zooming around in our solar system, one of the first questions a lot of people ask is how many are there, and how do we know that? We certainly haven’t found all the asteroids yet, so how can we be sure how many there really are, and how many more are left to discover?
The Wide-field Infrared Survey Explorer (WISE) mission captured this infrared view of an Earth-orbiting satellite (green streak, lower right), the Main Belt Asteroid Regina (which appears as a string of orange dots, upper right), and the Triangulum Galaxy (center left), one of the closest galaxies to our own Milky Way. In this heat-sensitive infrared image, the shortest wavelengths are color-coded blue, and the longest are shown as red. Regina was detected by the WISE’s mission asteroid-finding pipeline, known as NEOWISE. From its infrared signature, we can measure its size and the reflectivity of its surface. Regina is 47 km across, and its surface is as dark as black ink. It appears red in this image because it is much cooler than the stars, which are thousands of degrees. The string of red dots represents the multiple exposures of it that were collected by the WISE spacecraft. The satellite appears as a streak because it is much closer than the asteroid, so it appears to move much faster. Although the galaxy is moving incredibly fast, it is so far away that it appears stationary. Its blue stars are very hot, thousands of degrees, and the red regions highlight the cool, dusty locations where new stars are forming. Credit: NASA.