Out of This World! The Most Amazing Space Discoveries of 2016

2016 has been a bountiful year for space science. Before the calendar runs out, here's our list of the biggest space stories and events of the past 12 months.
There were monumental new discoveries, including the first-ever direct detection of gravitational waves, which gives scientists access to a whole new realm of information about cosmic events. This year, scientists also discovered a potentially habitable planet orbiting the star nearest to Earth's sun.

As always, there were also hurdles and setbacks. The ExoMars mission sent both an orbiter and a lander to the Red Planet, but the lander crashed into the planet's surface before it could begin its science mission. And multiple studies searching for signs of a particle that could explain mysterious dark matter turned up empty.

A planet around the nearest star to Earth's sun

The star Proxima Centauri lies just 4.2 light-years from Earth's sun — a stone's throw, cosmologically speaking. In August, scientists discovered a planet orbiting in Proxima Centauri's habitable zone, or the region where liquid water might exist on the planet's surface (and thus boosting the odds that life might have evolved there). This newly discovered planet, dubbed Proxima b, has a minimum mass of about 1.27 times Earth's mass, further increasing the possibility that this planet could be habitable.

Shortly after the discovery was announced, a group called Project Blue started fundraising to build a space telescope with the targeted mission of studying Proxima b and looking for signs of life there.

In April, the Breakthrough Foundation — whose board members include physicist Stephen Hawking, Facebook founder Mark Zuckerberg and entrepreneur Yuri Milner — announced an initiative called Breakthrough Starshot, which will aim to send a microchip-size spacecraft to another star. With the discovery of Proxima b, the Starshot project organizers announced that they would target this newfound planet, and potentially search for signs of life. The spacecraft would be accelerated with a massive (and expensive) laser system, and would still take about 20 to 25 years to reach Proxima b.

Ice deposit on Mars is bigger than Lake Superior

A massive ice deposit spanning a region the size of New Mexico was discovered in Mars' mid-northern latitudes. The deposit lies between 3 and 33 feet (1 to 10 meters) below the Red Planet's surface, it's between 50 and 85 percent water (the rest is dirt), and its total volume is about the same as that of Lake Superior, which holds about 2,900 cubic miles (12,100 cubic kilometers) of water.

The ice deposit could be useful if humans eventually settle on Mars. The region where the deposit was found, called Utopia Planitia, could be easily accessible by spacecraft because it is relatively flat and low-lying. The ice deposit was discovered using the Shallow Radar (SHARAD) instrument aboard the Mars Reconnaissance Orbiter.

Hubble spies potential water plumes on Europa

The Hubble Space Telescope has spied what appear to be plumes of water erupting from the surface of Jupiter's moon Europa. This icy satellite may harbor a liquid water ocean deep below its surface, and scientists think that ocean could have the right ingredients for life. NASA is currently planning to send an orbiting probe to study Europa in the 2020s.

If Europa is indeed spewing water from its ocean into space, that opens up the door for an orbiting mission to sample the water (without having to drill into the ice or even land) and look for hints of biology there. The Hubble telescope had spotted a plume erupting from Europa in 2012, but that detection seemed like it might have been a rare outlier, because no plume activity was observed in the intervening years.

Tabby's Star saga continues

In 2011 and 2013, a distant star known as KIC 8462852 (also known as Tabby's Star) appeared to dip in brightness as seen from Earth. This kind of brightness change can occur when an object such as a planet passes in front of a star, but planets orbit their parent stars on a regular time loop, and the changes in brightness coming from Tabby's Star were highly irregular. In 2015, a hypothesis emerged that captured the public imagination: Maybe an alien civilization had built some kind of megastructure around Tabby's Star, periodically blocking the star's light as seen from Earth. Alternative explanations (all of which seem far more likely) were produced, but there's not enough evidence to fully explain the mystery.

In 2016, the saga of Tabby's Star continued. New evidence suggested that the star's sporadic dimming might have been going on for a century. That makes it unlikely that the source of the dimming is a swarm of comets, but it could also make it unlikely that an alien megastructure is to blame. Further observations revealed that the star not only demonstrated periods of rapid brightening but was apparently decreasing in brightness overall.

That hasn't discouraged people from investigating the star further. The Breakthrough Listen initiative, which will spend $100 million over the next 10 years to hunt for signals possibly produced by alien civilizations, plans to study Tabby's Star with the 330-foot-wide (100 m) Green Bank Telescope in West Virginia. Astronomer Tabetha "Tabby" Boyajian of Yale University (for whom the star is nicknamed) was part of the team that originally identified the star's irregular behavior. Boyajian and her colleagues collected more than $100,000 through a Kickstarter crowdfunding campaign, and they plan to use those funds to pay for telescope time to study Tabby's Star further.