NASA / JPL-Caltech

This diagram illustrates the positions of Mars, Earth and the sun during a period that occurs about every 26 months, when Mars passes almost directly behind the sun from Earth's perspective. This arrangement, and the period during which it occurs, is called Mars solar conjunction.

By Mike Wall
Space.com

NASA's robotic Mars explorers are taking a cosmic break for the next few weeks, thanks to an unfavorable planetary alignment of Mars, the Earth and the sun.

Mission controllers won't send any commands to the agency's Opportunity rover, Mars Reconnaissance Orbiter (MRO) or Mars Odyssey orbiter from Tuesday through April 26. The blackout is even longer for NASA's car-size Curiosity rover, which is slated to go solo from April 4 through May 1.

The cause of the communications moratorium is a phenomenon called a Mars solar conjunction, during which the sun comes between Earth and the Red Planet. Our star can disrupt and degrade interplanetary signals in this formation, so mission teams won't be taking any chances.

"Receiving a partial command could confuse the spacecraft, putting them in grave danger," NASA officials explain in a video posted last month by the agency's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. [The Boldest Mars Missions in History]

Opportunity and Curiosity will continue performing stationary science work, using commands already beamed to the rovers. Curiosity will focus on gathering weather data, assessing the Martian radiation environment and searching for signs of subsurface water and hydrated minerals, officials said Monday.

MRO and Odyssey will also keep studying the Red Planet from above, and they'll continue to serve as communications links between the rovers and Earth. The conjunction will also affect the European Space Agency's Mars Express orbiter, officials have said.

Odyssey will send rover data home as usual during conjunction, though the orbiter may have to relay information multiple times due to dropouts. MRO, on the other hand, entered record-only mode on April 4. The spacecraft will probably have about 52 gigabits of data to relay when it's ready to start transmitting again on May 1, MRO officials have said.

Mars solar conjunctions occur every 26 months, so NASA's Red Planet veterans have dealt with them before. This is the fifth conjunction for Opportunity, in fact, and the sixth for Odyssey, which began orbiting Mars in 2001.

But it'll be the first for Curiosity, which touched down on Aug. 5, kicking off a two-year surface mission to determine if the Red Planet has ever been capable of supporting microbial life.

"The biggest difference for this 2013 conjunction is having Curiosity on Mars," Odyssey mission manager Chris Potts, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement last month.

Follow Mike Wall on Twitter @michaeldwall. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

• Amazing Mars Rover Curiosity's Martian Views (Latest Photos)
• Mars Explored: Landers and Rovers Since 1971 (Infographic)
• Mars Myths & Misconceptions: Quiz

Copyright 2013 Space.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

NASA / MOLA / Smithsonian

Mars' 600-mile Marte Vallis channel system is filled with young lavas that obscure the source of the channels. This map shows Marte Vallis against the background of an elevation map of the planet, based on readings from the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor.

A 3-D reconstruction of structures beneath the surface of Mars shows the 600-mile-wide footprint of a mega-flood that carved deep channels into the planet within the past 500 million years, scientists say.

Since that time, the evidence of the flood in a region known as Marte Vallis has been covered over by fresher lava flows. But a team of researchers pieced together the evidence by analyzing readings from a ground-penetrating radar instrument aboard NASA's Mars Reconnaissance Orbiter. The analysis was laid out Thursday on the journal Science's website.

"Our findings show that the scale of erosion was previously underestimated, and that channel depth was at least twice that of previous approximations," lead author Gareth Morgan, a geologist at the Smithsonian Institution's Center for Earth and Planetary Studies, said in a news release. "The source of the floodwaters suggests they originated from a deep groundwater reservoir and may have been released by local tectonic or volcanic activity. This work demonstrates the importance of orbital sounding radar in understanding how water has shaped the surface of Mars."

Over the past decade and a half, missions to Mars have provided ample evidence that the planet was once warmer and wetter than it is today. However, scientists say the most recent outflows of water came in brief, catastrophic bursts rather than as steady streams. The newly published research is consistent with that view.

Morgan and his colleagues used the orbiter's Italian-built Shallow Radar sounder, or SHARAD, to put Mars' subsurface geology through the radar equivalent of a CT scan. They found that the boundaries between the layers of fresher lava and the underlying rock traced a network of buried channels. The patterns and depths of those channels were characteristic of the canyons that would be cut by flowing water. Lots of flowing water.

The depth of the main channel was estimated at 226 to 371 feet (69 to 113 meters). "This is comparable with the depth of incision of the largest known megaflood on Earth, the Missoula floods, responsible for carving the Channeled Scabland of the northwestern United States," the researchers wrote. 

The Missoula floods occurred 12,000 to 18,000 years ago, due to a post-Ice Age warming trend, and discharged dammed-up water at a rate ranging up to 2.6 billion gallons per second. Morgan and his colleagues traced the Martian mega-flood to a radically different type of source: a fracture system in Mars' Cerberus Fossae region that apparently opened up to release water from miles beneath the Red Planet's surface. "It was a big crack in the ground, basically," Morgan told NBC News.

Smithsonian / NASA / JPL-Caltech / Sapienza Univ. of Rome / MOLA / USGS

A 3-D visualization shows the buried Marte Vallis channels. Marte Vallis consists of multiple perched channels formed around streamlined islands. These channels feed a deeper and wider main channel. The surface has been elevated and scaled by a factor of 1/100 for clarity. The area covered by this visualization is outlined by dotted lines in the global map above.

NASA / Goddard / Anna Brunner

NASA interns look down on Frenchman Springs Coulee in Washington state's Channeled Scablands. Researchers say the Martian mega-flood cut channels similar to those created thousands of years ago in the Channeled Scablands.

SHARAD's depth readings suggest that the channels had to have been cut somewhere between 10 million and 500 million years ago. Morgan said that makes the mega-flood channels "much younger" than the geological features being studied by NASA's Curiosity rover in a different region of Mars. Curiosity's science team wants to find out whether Mars had liquid water and the other conditions conducive for life 3 billion years to 4 billion years ago. On the surface, at least, those conditions were long gone by the time the Cerberus Fossae mega-flood washed over Marte Vallis.

More about Mars:

• Curiosity rover finds itself in ancient riverbed
• Did life on Earth get started on Mars?
• Cosmic Log archive on Mars

In addition to Morgan, the authors of "3D Reconstruction of the Source and Scale of Buried Young Flood Channels on Mars" include Bruce A. Campbell, Lynn M. Carter, Jeffrey J. Plaut and Roger J. Phillips.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

NASA / JPL-Caltech / ASU

Three Martian whirlwinds, known as dust devils, whirl in this picture captured by NASA's Mars Reconnaissance Orbiter on Feb. 11.

It's eerie enough to see one whirlwind swirling across the Martian surface, but three? Get out your 3-D glasses and spot the three dust devils rising from Amazonis Planitia, as seen by the high-resolution camera aboard NASA's Mars Reconnaissance Orbiter.

These mini-twisters are analogous to the dust devils that are whipped up on sunny afternoons on Earth, due to the rise of hot air through a low-pressure pocket of cooler air above it. In February, the Mars orbiter spotted a couple of prominent examples of the phenomenon that rose as high as 12 miles into the Red Planet's thin atmosphere. These three dust devils aren't nearly as big, but seeing them simultaneously in one 3-D picture gives you an idea just how active the wind patterns on Mars can get.

"The active dust devils seem to float above the surface," says Arizona State University's Alfred McEwen, principal investigator for the camera, known as the High Resolution Imaging Science Experiment or HiRISE. "There are also some bright lines present ... those are the tracks of dust devils that passed through this region in the prior two weeks."

For more from Mars, check out the HiRISE website — and as long as you have your 3-D glasses out, take a look at HiRISE's 3-D image gallery. What? You don't have your 3-D glasses yet? This NASA webpage lists some online vendors. While you're at it, think about picking up some sun-viewing spectacles for the May 20 annular solar eclipse. On Friday, I'll be giving away a combo pack of 3-D glasses and eclipse glasses as the prize in our weekly "Where in the Cosmos" photo contest; watch for that on the Cosmic Log Facebook page.

More about Mars:

• NASA re-creates dust devil in 3-D
• Video: Watch a Martian twister spin
• Twisty dust devil captured on Mars
• Watch a dust devil spin in the Martian arctic
• Slideshow: Greatest hits from the Red Planet

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.

NASA / JPL-Caltech / Univ. of Arizona

A towering dust devil casts a serpentine shadow over the Martian surface in this image, acquired on Feb. 16 by the High Resolution Imaging Science Experiment on NASA's Mars Reconnaissance Orbiter.

A Martian mini-tornado caught on camera by NASA's Mars Reconnaissance Orbiter brings new meaning to the word "twister."

This isn't the first dust devil to show up on Martian imagery. The whirlwinds have been photographed by NASA probes for more than 30 years, and in some places, the Red Planet's landscape is heavily crisscrossed by dust devil tracks. In 2005, the Spirit rover's time-lapse view of multiple dust devils was made into a movie. But this picture, taken on Feb. 16 as the orbiter passed over the Amazonia Planitia region of northern Mars, has to rank among the most artistic of the dust devil delights.

Scientists estimate that the dust devil rose to a height of more than half a mile (800 meters), with a plume that's about 30 yards (meters) in diameter. A westerly breeze adds a delicate arc to the plume, and the afternoon sun creates a curving, stretched-out shadow.

Dust devils on Mars, like their cousins on Earth, are spinning columns of air that are made visible by the dust they stir up. They typically arise on a clear day when the ground is heated by the sun. As the atmospheric layer near the surface warms, air rises through a pocket in the cooler layer above it, taking on a spin when the conditions are just right.

Martian air is much thinner than our earthly atmosphere, and composed almost entirely of carbon dioxide. But the Red Planet's winds can still pack a huge punch. Over the years, NASA's rovers have benefited from wind-driven "cleaning events" that sweep the dust off their power-generating solar panels. Last month, the Opportunity rover underwent a slight cleaning that put it in a better position to endure the Martian winter — which just goes to show that a devil can be an angel on the Red Planet.

More from Mars:

• The Mars rover stays in the picture
• Watch a dust devil spin in the Martian arctic
• Slideshow: Greatest hits from the Red Planet

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.