The planet Mercury has no moons, but why is that the case? The reason is due to a combination of its small size, orbit, and weak gravity.

Still looking for the perfect calendar for 2016? Don't start the year without the new Year In Space Wall Calendar!

Missions to Mars, Jupiter and asteroids are on tap in 2016. Back here on Earth, we may just see the first direct detection of gravitational waves, and some serious exoplanet and SETI hunts get underway... and could 2016 become the year of the heavy lift rocket? Here's the big space stories we're watching in 2016.

Mountains are formed by geological and tectonic forces, resulting in massive formations that are amazing and awe-inspiring.

KENNEDY SPACE CENTER, FL – Buildup of the first of Boeing's CST-100 Starliner crew spaceships is ramping up at the company's Commercial Crew and Cargo Processing Facility (C3PF) - the new spacecraft manufacturing facility at NASA's Kennedy Space Center.

Gravity is a fundamental force in our universe. And on the planets in our Solar System, it is dependent on the size, mass, and density of the body.

As history closes in on 2015, assembly of NASA's James Webb Space Telescope (JWST) reached a historic milestone as the installation of the primary mirrors onto the telescope structure reached the halfway point to completion and marks the final assembly phase of the colossal observatory.

Comets, conjunctions, eclipses and more await astronomy fans worldwide in 2016, as well as a fine opposition of Mars and a rare transit of Mercury across the face of the Sun. Get ready for astronomy 2016! Camping out under dark skies. Image credit and copyright: Michelle Nixon/MNixon Photography

Elon Musk's dream and ultimate goal of establishing a permanent human presence on the Red Planet in the form of "A City on Mars" took a gigantic step forward with the game changing rocket landing and recovery technology vividly demonstrated by his firm's Falcon 9 booster this past Monday, Dec. 21

Just in time for the holidays, NASA's Curiosity rover is celebrating Christmas 2015 at a Red Planet Paradise - spectacular "Namib Dune." And she marked the occasion by snapping her first ever color self-portrait with the mast mounted high resolution Mastcam 34 mm camera.

A nebula is a common feature of our universe, consisting of gas particles and dust which are closely associated with stars and planetary formation.

NASA managers have just made the difficult but unavoidable decision to scrub the planned March 2016 launch of the InSight lander, the agency's next mission to Mars, by at least two years because of a vacuum leak that was just detected in the probes flawed seismometer instrument which cannot be fixed in time.

"There and back again," said SpaceX CEO and founder Elon Musk after the amazing successful 'Return to Flight' launch of the firms Falcon 9 rocket and history making vertical return landing at Cape Canaveral, Fla, on Monday evening, Dec. 21.

Like all stars, our Sun has a life-cycle that began with its birth (4.57 billion years ago) and will end in approximately 6 billion years.

"The Falcon Has Landed!" gushed exuberant SpaceX officials following tonight's (Dec 21) history making ground landing of the firms spent Falcon 9 boost stage barely 10 minutes after if launched on a critical mission to deliver a constellation of communications satellites to Earth orbit.

All is "GO" in the final hours of the countdown to leading up to tonight's, Dec. 21, the high stakes blastoff of an upgraded SpaceX Falcon 9 rocket from Cape Canaveral on its 'Return to Flight' mission carrying a flock of commercial satellites to orbit that also features a breathtaking and history making flyback of the rockets first stage to a soft landing on the ground that could open a majestic era of Rocket Reusability - if all goes well.

The waxing gibbous Moon will occult the bright star Aldebaran in the constellation of Taurus the Bull this Wednesday evening one more time in 2015. Observers across Europe and northern Asia will witness the event. Here's our guide to observing the occultation and more.

A "significantly upgraded" SpaceX Falcon 9 rocket stands erect on the Florida space coast today, Sunday, Dec. 20, and is poised to make history Monday evening with a spectacular nighttime blast off and daring first ever surface landing attempt of the boosters first stage at Cape Canaveral Air Force Station, that could be accompanied by sonic booms - if all goes well.

SpaceX CEO Elon Musk announced today (Dec. 19) that his company plans to launch an upgraded version of its Falcon 9 rocket on Sunday night, Dec. 20, from Cape Canaveral, Florida, for the first time since it failed in flight six months ago on a mission for NASA to the space station, after successfully completing a test of the rockets engines late Friday night.