This image released by NASA shows "Curiosity's" work site on Mars.
Rovers resumed their communication tasks after a month-long solar blackout.
CAPE CANAVERAL, Fla. -- Two robotic U.S. rovers are back in business on Mars after a monthlong solar blackout that blocked communications with engineers back on Earth.
"Can you hear me now? Conjunction is over. I have a clear view of Earth & am back to work!" NASA's Curiosity rover tweeted last week.
The car-sized Curiosity rover and its smaller cousin Opportunity, along with U.S. spacecraft orbiting Mars, resumed full operations after the conclusion of what scientists call a "solar conjunction."
The sun in early April moved into an orbit directly between Earth and Mars, interfering with communications between the planets.
Solar flares and charged particles spewing from the sun blocked radio signals, so the spacecraft went on a Martian "spring break."
The rovers stopped roving and performed only limited scientific work, such as observing weather and measuring radiation. But, otherwise, the rovers and the U.S. orbiters were placed in a state of scientific hibernation for about 30 days.
During the past month, the alignment of the sun, Earth and Mars has gradually shifted, and engineers now are back in touch with the fleet of U.S. Mars explorers.
"Back in Action: Opportunity is out of stand-by mode & is now executing a new command sequence" sent by engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., the Opportunity team tweeted.
Curiosity is resuming scientific studies in an area called Yellowknife, a waypoint in a trek that eventually will lead to the base of Mount Sharp. The three-mile-high mountain features layers or sedimentary rock that should shed light on the geological history of Mars.
Opportunity is getting back to work on the western rim of Endeavour Crater, a 14-mile-wide bowl-shaped cavity in the western equatorial region of the planet. Outcrops on the rim comprise mineral that might have been formed under wet conditions in the early history of Mars.
Curiosity was launched from Cape Canaveral Air Force Station in late November 2011 and arrived on the surface of Mars last August. Operating inside Gale Crater in the planet's eastern equatorial region, its $2.5 billion mission aims to determine if Mars is, or ever was, habitable.
Opportunity blasted off from Cape Canaveral in 2003 and landed on Mars in January 2004. Designed to operate on the planet's surface for just 90 days, Opportunity still is roving around a flat region called Meridiana Planum. Data beamed back from rover instruments indicate the area once was awash with water.
Opportunity's twin, the Spirit rover, operated in Gusev Crater from January 2004 through March 2010.
NASA operates two spacecraft in Martian orbit - the Mars Reconnaissance Orbiter and the Mars Odyssey spacecraft. The U.S. also provided scientific instruments for the European Space Agency's orbiting Mars Express spacecraft.