NASA launched a new space-weather mission, scientists found evidence of a hydrothermal system on Saturn's ocean-bearing moon Enceladus and three astronauts returned safely to Earth after nearly six months aboard the International Space Station. Here's a look at Space.com's top stories of the week:

NASA space weather mission takes flight

NASA launched its Magnetospheric Multiscale (MMS) mission, which consists of four satellites that will study energy eruptions in Earths magnetic field caused by space weather. MMS blasted off Thursday night (March 12) from Cape Canaveral, Florida, aboard a United Launch Alliance Atlas V rocket. [Full Story: Spectacular Night Launch Sends NASA Satellites on Hunt for Magnetic Collisions]

A hydrothermal system on Enceladus

Scientists have found evidence of active hydrothermal vents on Saturn's ice-covered moon Enceladus. Conditions deep in Enceladus' subsurface ocean may therefore be similar to those that gave rise to the first life on Earth. [Full Story: Hot Springs on Saturn's Moon Enceladus Powered by Hydrothermal Vents]

Spaceflyers come home

A Russian Soyuz spacecraft touched down on the steppes of Kazakhstan Wednesday night (March 11), wrapping up a nearly six-month stint aboard the International Space Station for NASA astronaut Barry "Butch" Wilmore and cosmonauts Alexander Samokutyaev and Elena Serova. [Full Story: US-Russian Space Crew Returns to Earth After 167 Days in Orbit]

Happy birthday, Kepler!

NASA's prolific Kepler space telescope, which has discovered more than half of all known planets beyond our solar system, just celebrated six years in space. The prolific planet hunter blasted off on March 6, 2009. [Full Story: Happy Birthday, Kepler! NASA Planet Hunter Marks 6 Years in Space]

NASA test-fires booster for Space Launch System megarocket

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Best Space Stories of the Week March 15, 2015