The planet Mars was a bright red “star” in our sky on August 5, 2012, when the newest Mars rover Curiosity made its dramatic descent to the surface of the Red Planet. But by early April 2013, when Mars and Venus will sweep near each other after sunset, what otherwise would be an awesome conjunction of two cool planets will lost in the sunset glare. Mars has now left the evening sky, on its way to passing behind the sun as seen from Earth on April 18. Around the time this happens – for 17 to 21 days in April, 2013 – NASA will be forced to temporarily suspend its exploration of Mars.
NASA said in a press release on March 20:
The sun can easily disrupt radio transmissions between the two planets during [Mars and the sun's] near-alignment [as seen from Earth]. To prevent an impaired command from reaching an orbiter or rover, mission controllers at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., are preparing to suspend sending any commands to spacecraft at Mars for weeks in April. Transmissions from Mars to Earth will also be reduced.
From the standpoint of earthly observers, Mars conjunctions are not identical from year to year. As seen from Earth, Mars could be nearer to the sun at a given year’s conjunction, or farther away, and the sun might be in an active or a quiet phase of its 11-year cycle of activity.
This year, Mars and the sun will be relatively close together on the sky’s dome at conjunction, in contrast to some other years. Meanwhile, the sun is near the peak of its cycle, albeit a mild peak, in contrast to some. So the chances for radio interference between Earth and Mars are good.
But the biggest difference for this 2013 conjunction is having Curiosity on Mars, according to NASA scientists. Odyssey – a robotic spacecraft orbiting Mars since 2001 – and the Mars Reconnaissance Orbiter – orbiting Mars since 2006 – relay almost all data coming from Curiosity and an older rover, Opportunity. NASA said:
Transmissions from Earth to the orbiters will be suspended while Mars and the sun are two degrees or less apart in the sky, from April 9 to 26, with restricted commanding during additional days before and after.
Bottom line: NASA mission controllers will suspend Mars exploration via spacecraft for 17 to 21 days in April, 2013. At that time, Mars will be behind the sun as seen from Earth. The space engineers are worried that interference from the sun could impair radio transmissions between Earth and Mars, causing the spacecraft to execute a faulty command.