This artist's conception illustrates a giant planet floating freely without a parent star. Astronomers recently uncovered evidence for such lone worlds, thought to have been booted from developing star systems. The sun may have captured such a planet, which new work shows may reside at the edge of the solar system.
Every year at Discovery News we reach out to our loyal readers to find out what
favorite space stories were for 2013. These aren't necessarily the biggest science stories nor the biggest discoveries; they are the stories that engaged
over the past 12 months. 2013 has been nothing short of epic for adventures in space -- but after pooling your nominations and taking web traffic into consideration, you voted and there is a clear winner for the year. So, what was the "Reader's Choice: Favorite Space Story of 2013"?
Read on to find out.
Bill Saxton; NRAO/AUI/NSF; NASA/Hubble; Raghvendra Saha
How do you go about finding the coldest place in the universe? Well, it helps if you have a stonking great radio telescope to scan the skies. On Oct. 23, we reported on a chilly discovery by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. ALMA had zeroed in on the Boomerang Nebula and gauged its temperature. Not only was the dark cloud of space dust cold, it was
the coldest object ever spotted in the Cosmos
, barely tipping the temperature scale at one Kelvin -- that's –458 degrees Fahrenheit or –272 degrees Celsius.READ MORE: This Is The Coldest Place In The Universe
NASA's Kepler space telescope has literally transformed our understanding of planetary systems in our galaxy. Although the mission has suffered some serious setbacks this year, Kepler data continue to reveal smaller and smaller worlds circling their stars in orbits not too dissimilar to Earth's orbit around the sun. So that raises the question: How many 'habitable' worlds are out there? On Nov. 4, astronomers announced their answer:
. Yes, there are likely 10 billion habitable exoplanets in the Milky Way.READ MORE: Galaxy Hosts 10 Billion 'Habitable' Earth-Size Worlds
Oh Comet ISON, what the heck happened? In September 2012, Comet ISON was discovered by Russian astronomers and it was quickly revered as the "Comet of the Century." It was a virgin comet, fresh from the Oort Cloud, and it was destined to barrel past the sun to become one of the brightest objects in the sky. The world rallied behind the comet. Daily comet health updates read like war reports. The media cheered ISON on. As it got closer and closer to the sun everything was looking good! The comet was holding it together! It was going to make it! Until... it didn't. The Thanksgiving Day roast proved to be too much for this famous comet. Although there were signs that ISON's nucleus survived the encounter, the sun's extreme heat and tidal shear likely ripped it to shreds. This cosmic story may not have had a a happy ending, but ISON was no turkey; it was mainstream news for months, proving that mankind's fascination with astronomy is alive and well.READ MORE: ISON's Ghost: 'Comet of the Century' is Now Ex-Comet
On Dec. 14, China became only the third nation ever to softly land a robot on the moon, a feat that hasn't been achieved since the Soviet Luna 24 sample return mission in 1976. The mission, Chang'e 3, lowered its six-wheeled rover, "Yutu" ("Jade Rabbit"), to the lunar surface, where it's currently taking a spin in the lunar regolith. Jade Rabbit expected to carry out science for at least 3 months.READ MORE: China's Rover Rolls! Yutu Begins Moon Mission
NASA, ESA, and M. Kornmesser
Few worlds inspire the imagination quite like Europa, one of Jupiter's largest moons. The icy crust protects a sub-surface ocean of liquid water, heated from the inside by tidal interactions with the gas giant. Spectroscopic observations of Europa's ice reveal a dynamic interplay between the ocean and surface, leading to the theory that nutrients and oxygen can be cycled down below. All these factors have led astrobiologists to call for a mission to the moon; a mission that could reveal a Europan biosphere -- potentially hosting
. Now, in new observations by the Hubble Space Telescope, plumes of water vapor have been discovered venting into space. Wouldn't it be awesome if we could fly a spacecraft through that plume to see if any biological material has hitched a ride? Sadly, NASA's planetary sciences budget has been slashed, likely sidelining that bold idea for many years to come.READ MORE: Hubble Discovers Water Plumes Over Europa
In a "Reader's Choice" first, I'm exercising my editorial muscle and including a multidecade story that reached its satisfying conclusion this year -- one of my favorite stories of 2013.
The hunt for the Higgs Boson, the "last" component of the Standard Model of physics, came to an end in March when physicists analyzing data from the Large Hadron Collider, near Geneva, Switzerland,confirmed that the particle had been discovered
. This concluded the "99 percent certainty" discovery announcement of July 2012 that the particle was, without a shadow of a doubt,
Higgs boson. The Higgs boson is the "exchange particle" that mediates the Higgs field, endowing all matter in the universe with mass. The discovery quickly led to the original Higgs boson theoretical physicists -- Francois Englert of Belgium (pictured here, left) and Peter Higgs of the United Kingdom (right) --being awarded the 2013 Nobel Prize for Physics
. From Higgs field theory in the 1960s, to the construction of the most complex machine humans have ever conceived (the LHC), to the boson's ultimate discovery, it's one of the biggest discoveries and most fascinating physics journeys of our time.READ MORE: Particle 'Consistent' With Higgs Boson Discovered
David A. Aguilar (CfA)
The Kepler Space Telescope has discovered some weird exoplanets, worlds that are rewriting well-established planetary formation theories. However, the "Award for Weirdest" will likely go to Kepler-76b, the exoplanet that shouldn't even exist. It's small, it's rocky and it orbits its star every 8.5 hours. The location for this hot lava world has astronomers scratching their heads -- how could a world only 20 percent bigger than Earth have formed so close to a star?READ MORE: Kepler-78b: Mystery Exoplanet Shouldn't Even Exist
Reader's Choice 2013
As the first Canadian to command the International Space Station (ISS), astronaut Chris Hadfield had more than his fair share of responsibilities on the orbiting outpost. But that didn't stop the Ontario native from sharing his awesome experiences with Earth. For his infectious enthusiasm for bringing orbital sciences down to Earth during his five-month stay on the ISS, engaging millions in the process and starring in the first ever space music video, Discovery News selected Hadfield for the first ever "2013 DNews Person of the Year."READ MORE: Chris Hadfield: DNews Person Of The Year
Reader's Choice 2013
NASA's Mars rover Curiosity continues to blow us away with the incredible science it's doing in Gale Crater, gradually unraveling the mysteries of the Red Planet's habitable past one rock at a time. But on Dec. 9, mission scientists announced a groundbreaking discovery: the rover had uncovered an ancient lake bed that would have once been perfectly suited for colonies of simple, rock-eating microbes found in caves and hydrothermal vents on Earth. Although Mars rovingis taking its toll
on the robot's wheels, we can expect many more incredible science discoveries in the months and years to come.READ MORE: Mars Rover Finds Ancient Life-Supporting Lakebed
This date -- Feb. 15, 2013 -- will be a date forever remembered as when Earth suffered a cosmic flesh wound. During the chilly morning commute in the city of Chelyabinsk, Russia, a fireball -- or "superbolide meteor" -- lit up the sky, outshining the dawn sunlight. The fireball was caused by a 12,000–13,000 ton asteroid slamming into our atmosphere at 60 times the speed of sound. The shockwaves generated by the atmospheric impactcaused 1,500 injuries (mainly from blown-out windows) and cost millions of dollars in property damage
. The Russian meteor event -- the largest in modern history and the first documented case of a large fireball explosion over a populated region -- strengthened arguments for improved asteroid impact mitigation strategies. The Chelyabinsk event proved that it's not a matter of if, it's a matter of
we'll get hit again.READ MORE: Huge Fireball Explodes Over Russia
Voyager 1 has gone interstellar!
After 35 years and 13 billion miles, scientists announced on Sept. 12 that the veteran spacecraft has left the heliosphere -- the sun's sphere of magnetic influence -- and entered interstellar space. This is the first man made spacecraft to ever achieve such a feat, officially making us a civilization that has the technology to explore the universe beyond our interplanetary front door. This achievement appears to have inspired our readers, propelling it to the #1 spot of this year's "Reader's Choice." As Voyager 1 (and her sister spaceship Voyager 2) are showing us,
space is vast
. But they also prove that accessing the space between the stars is not an impossible task. But if we are to become a true interstellar race, we'll need a faster mode of transportation before we realize our star-trekking dreams.READ MORE: Voyager: Goodbye Solar System, Hello Interstellar Space
The hunt for the hypothetical "Planet X" has been fruitless so far, but that doesn't mean astronomers are calling it off.
A new analysis of data collected by NASA's Wide-Field Infrared Survey Explorer (WISE) spacecraft revealed no sign of the mysterious Planet X hypothesized to exist in the outer solar system. But scientists are keeping up the search for a planet or dim star far from the sun.
"I think astronomers will continue to search for a distant companion to the sun with every new, deeper survey," Kevin Luhman of the University of Pennsylvania told Space.com by email. Luhman, who studies low-mass stars and "failed stars" known as brown dwarfs, recently published the results of his search for Planet X using WISE. [Images from NASA's WISE Space Telescope]
"We have a natural desire to better determine the contents of our solar system," Luhman said. "There's a vast volume of space in the outer solar system, and we would like to know what's out there."
And a recent find may give a boost to the hunt for Planet X. On Wednesday (March 26), researchers announced they had discovered a dwarf planet orbiting the sun in a distant, largely unexplored region known as the inner Oort Cloud.
Further, the orbits of the newfound object, known as 2012 VP113, and some of its neighbors are consistent with (though by no means proof of) the existence of a planet-size "perturber" far from the sun — perhaps so distant that it cannot be detected with current instruments.
An Unseen Companion
For more than a century, astronomers have considered the possibility that another massive body exists in the outer solar system.
Percival Lowell coined the term "Planet X" at the turn of the 20th century to refer to an undiscovered large planet that could be responsible for perturbing the orbits of Uranus and Neptune. More recently, the idea grew to incorporate a possible dwarf-star companion to the sun, nicknamed "Nemesis."
Orbit diagram for the outer solar system. The sun and terrestrial planets are at the center. The orbits of the four giant planet Jupiter, Saturn, Uranus and Neptune are shown by purple solid circles. The Kuiper Belt (including Pluto) is shown by the dotted light blue region just beyond the giant planets. Sedna's orbit is shown in orange while 2012 VP113's orbit is shown in red. Both objects are currently near their closest approach to the sun. They would be too faint to detect when in the outer parts of their orbits. Scott S. Sheppard: Carnegie Institution for Science
In the 1980s, scientists suggested that a solar companion could be responsible for causing mass extinctions on Earth every 26 million years. They theorized that a small, dim star or a large brown dwarf -- a body larger than a planet but too small to ignite the fusion reactions that power stars -- could periodically pass through the Oort Cloud, the faraway comet repository that surrounds the solar system.
Gravitational tugs from this body could send a rain of comets hurtling toward the inner solar system, where some would collide with Earth and threaten any life that existed. [Wipe Out: History's Most Mysterious Extinctions]
The Infrared Astronomical Satellite (IRAS), the first space telescope to scan the entire sky in the infrared, collected a wealth of data in the early 1980s but found no sign of the putative distant object. More detailed data came back from NASA's Two Micron All-Sky Survey (2MASS) a decade and a half later, with the same result.
But that didn't end the search for the mysterious body. A 1999 study, for example, claimed to find subtle anomalies in the orbits of comets — possible evidence for a distant solar companion. A follow-up study by the same authors in 2011 made the same claim. The team of astronomers suggested that the oddities could be the result of a gas giant planet that they nicknamed "Tyche."
Still scanning the heavens
Most astronomers today don't give much credence to the claims of historical evidence for a companion star or distant planet, Luhman said. Yet the hunt continues, because the possibility such a body could exist is always there. (An Earth-size object would likely be undetectable with current instruments if it lay about 250 Earth-sun distances away, researchers say.)
The recent results from WISE provide an even more detailed look at cool bodies within the solar system. Luhman's work, published in The Astrophysical Journal, found no sign of Saturn-size bodies to a distance of 10,000 times the Earth-sun distance. (The distance from Earth to the sun, known as an astronomical unit or AU, is about 93 million miles, or 150 million kilometers).
The survey also sought Jupiter-like and larger bodies, which would include brown dwarfs and low-mass stars, as far away as 26,000 AU. It turned up no hint of the hypothesized body.
If scientists hadn't suggested that an unseen star or planet could be affecting life on Earth, would astronomers still search for Planet X? Luhman thinks so.
"Even if no one had previously claimed to find evidence of a large body in the solar system, one would naturally search for an object of that kind with every new all-sky survey that is able to see fainter objects than the previous survey," he said.
Improving technology could make the difference when it comes to turning up a solar companion. According to Luhman, there is a small chance that a distant companion to the sun could have been missed if it was aligned close to a bright star. Data from the bright star could then have overwhelmed the companion, much as the sun overpowers a flashlight beam.
A companion could also have escaped detection by WISE if it has a relatively small mass and lies extremely far away. The smaller and dimmer an object is, the harder it becomes to spot as it draws farther away.
"I think people are amazed by the fact that we can detect galaxies billions of light-years away, and yet there are parts of our own solar system that remain uncharted and unexplored," Luhman said.
More from SPACE.com:
Our Solar System: A Photo Tour of the Planets
Killer Asteroids: We're WISE to You Now!
Quiz: How Well Do You Know Our Solar System?