An artist's rendition of the gigantic ring system circling J1407b. Courtesy of Ron Miller hide caption

An illustration of Rosetta just before Friday's expected landing on the comet known as 67P/Churyumov-Gerasimenko. The final approach aims to be only at "walking speed," mission specialists say, but that's enough to tip the antenna away from Earth. ATG medialab/ESA hide caption

An artist's depiction of the surface of the planet Proxima b as it orbits the red dwarf star Proxima Centauri, the closest star to our solar system. The planet is a bit more massive than Earth, scientists say, and circles its star once every 11 days. ESO/M. Kornmesser/Nature hide caption

The Japanese Subaru Telescope on Mauna Kea in Hawaii has the right attributes for searching for Planet Nine. National Astronomical Observatory of Japan hide caption

This illustration show's NASA's Juno mission approaching Jupiter. Juno used distant stars to chart its course across the void. NASA/JPL-Caltech hide caption

Launched from Earth in 2011, the Juno space probe has nearly reached Jupiter. If all goes as hoped, the probe will repeatedly dive between the planet and intense belts of charged particle radiation, in an orbit that will take it from pole to pole. JPL/NASA hide caption

The imagined view from "planet nine" back toward the sun. Astronomers think the huge, distant planet is likely gaseous, similar to Uranus and Neptune. Caltech/R. Hurt (IPAC) hide caption

The imagined view from Planet Nine back toward the sun. Astronomers think the huge, distant planet is likely gaseous, similar to Uranus and Neptune. Caltech/R. Hurt (IPAC) hide caption

A still image from a video produced by the To Scale Series shows a model of the solar system in which planets orbit the sun on a dry lakebed in Nevada. To Scale Series hide caption

A portrait of Pluto (right) and its moon Charon in a colorized, composite image made July 11 during the final approach of the New Horizons spacecraft. Astronomers are eager to get a much closer view of the icy world Tuesday. NASA-JHUAPL-SWRI hide caption

Stars over the Cerro Tololo Inter-American Observatory in Chile. Sheppard and Trujillo used the new Dark Energy Camera (DECam) on a telescope there to find the distant dwarf planet 2012 VP 113. Reidar Hahn/Fermilab hide caption

In this artist concept provided by NASA, the MAVEN spacecraft approaches Mars on a mission to study its upper atmosphere. AP hide caption

Composite video showing what the Earth's sky would look like if Saturn orbited our planet at the same distance as our moon. Screenshot/Yeti Dynamics/YouTube hide caption

An illustration of what the Philae lander will look like at work on Comet 67P/Churyumov-Gerasimenko. AOES Medialab/ESA hide caption

Part of the ALMA array on the Chajnantor plateau of Chile points skyward to the Milky Way, our own galaxy. The center of our galaxy is visible as a yellowish bulge crossed by dark lanes, which are themselves huge clouds of interstellar dust. José Francisco Salgado/ESO hide caption