Martian armada. NASA currently has five spacecraft studying Mars close-up. But when it comes to the amount of information returned to Earth, the Mars Reconnaissance Orbiter (MRO) stands above all others. On average, it returns about 80,000 megabits of data each martian day, or sol (one sol equals 1.03 Earth days). This graphic compares MRO with the other three probes currently on extended missions. Because data rates vary with Mars’ distance from Earth — in the same way a wireless connection slows down with distance — it does not include the recently arrived MAVEN orbiter.