Astronomers have continued to cast their eyes to the heavens, with bigger and better telescopes and as much passion as ever this year, but some of the coolest findings of 2008 were right in our own backyard — or at least looked like they were.
From worlds nearby like Mercury and Mars to those beyond our solar system, planetary science saw a boon. As for extrasolar planets, astronomers bagged at least 50 newbies this year.
"It's been a very exciting year for exoplanet discoveries," said Michael Liu, an astronomer at the University of Hawaii.
What's responsible for the surge of exoplanet detections?
"The big picture is that a wide variety of new technologies, both instruments on existing telescopes and new dedicated telescopes, are really allowing astronomers to do much more sensitive measurements, and thus leading to a real bonanza of discoveries," Liu told SPACE.com.
And there's more. Here are five favorite findings in astronomy for 2008:
1. Alien worlds
With the extrasolar planet tally now well above 300, astronomers seem to be on track for spotting another Earth (the astronomical jackpot) before long.
Along the way this year, a jaw-dropping announcement came in November when two teams of astronomers reported they had snapped direct images of exoplanets.
Geoffrey Marcy of the University of California, Berkeley, calls the images "the most spectacular thing in 2008."
"In my own professional opinion this is by far the most definitive picture of a planet ever taken," Marcy said during a telephone interview, referring to the direct image by the Hubble Space Telescope of the planet called Fomalhaut b.
The gold rush of exoplanet discoveries this year boils down to new techniques and observatories as well as energetic astronomers involved, Marcy said.
Some other highlights include: the least-massive planet, weighing in at just three times the mass of Earth; the hottest planet, with temperatures reaching about 4,000 degrees Fahrenheit (2,200 degrees Celsius); and three so-called super-Earths orbiting a star.
Astronomers like Marcy predict the upcoming year will bring us even closer to detecting Earth's twin.
For instance, NASA's Kepler mission is scheduled to launch in March with the goal of finding rocky planets about the size of Earth that orbit within the habitable zone of their host stars where liquid water and life might exist. Stay tuned.
2. Martian life?
The red planet has gotten celebrity treatment this past year, with the touchdown of NASA's Phoenix Mars Lander in May, the continuing presence of the Mars Exploration Rover twins (Spirit and Opportunity) and NASA's Mars Reconnaissance Orbiter (which has imaged nearly 40 percent of the planet).
A major goal of such missions has been to find signs of past or present liquid water, the main ingredient for life. That's why Phoenix snagged a star-studded headline when the lander collected water ice near Mars' north pole this year.
Earlier in the year, Spirit found deposits of silica in Gusev Crater, suggesting, scientists said, that hot water once flowed through the Martian soil in hydrothermal vents.
As on Earth, these hydrothermal vents may have once harbored life. The discovered silica could preserve fossils of such ancient life if it did indeed exist there.
Just in from MRO — evidence of carbonates on the Martian surface. Since carbonates can't survive in acidic, harsh conditions, the mineral finding suggests any microbes crawling around when Mars was wet could've enjoyed a cushy existence.
3. Dark energy
Scientists were hot on the trail this year of a mysterious "force" called dark energy that has been expanding the universe at an increasing pace and was only discovered about 10 years ago.
Though, admittedly, scientists say they are more than a few years away from solving the puzzler of what dark energy is, a new method this year confirmed its existence, suggesting the force is stifling the growth of galaxies in the universe.
Basically, in an expanding universe dominated by dark energy, galaxies fly away from one another rather than mingle and merge.
These results also suggest dark energy takes the form of what Einstein called the cosmological constant — a term in Einstein's theory of general relativity that represents the possibility of empty space having a density and pressure associated with it.
4. Black hole antics
Black holes are so dense that nothing, not even light, can escape their gravitational grips. Though invisible, astronomers have inferred the presence of the dark behemoths from their effects on nearby objects. And this year, it seems, all the crazies came out of their cosmic closets.
Take the fastest-spinning black hole, found to whirl around at speeds approaching the speed of light.
And when it comes to obesity, one black hole could've gobbled up 18 billion suns. This giant would dwarf the smallest black hole found this year, weighing in at about 3.8 times the mass of our sun and spanning just 15 miles (24 km) in diameter.
Researchers also found this year that some supermassive black holes, which reside at the centers of many or all galaxies, spew out giant bubbles from the tips of their jets. (As material falls into the gravitational clutches of a black hole, the energy can be spit out as jets of radiation and high-speed particles.)
The bubbles ultimately pop, spilling their gaseous guts. Turns out, the hot gas keeps the black hole and its galaxy from ballooning to mega sizes.
Black holes can also take the form of "masked fugitive." Computer simulations revealed that when two black holes merge, the energy produced can kick the newly merged black hole clear out of its galaxy.
Also, for the first time this year, scientists detected such a rogue black hole racing along at 5,900,000 mph (2,650 kilometers per second).
5. Solving Mercury mysteries
More than half of our solar system's smallest planet (Pluto once took this honor), Mercury, had remained a mystery until this year. On Jan. 14, NASA's MESSENGER probe made its first flyby of Mercury, beginning a mission to image the entire planet.
From the get-go, the probe sent back intriguing images, including clear evidence for volcanoes. Images of the Caloris basin showed hints of lava flows and the presence of a shield volcano larger than the state of Delaware, with gently sloping sides.
Mercury is indeed shrinking as its iron-rich core slowly cools. Scientists had speculated this much from images taken during the Mariner 10 mission in 1974.
But MESSENGER images showed more faults than did Mariner 10, suggesting the strain from the planet's contraction was at least one-third greater than originally thought.
More to come: The thousands of images and other data collected by MESSENGER could also shed light on other Mercury mysteries, including the planet's relatively giant core, which makes up about two-thirds of the planet's mass.
One idea is that huge impacts hundreds of billions of years ago might have stripped the innermost planet of its original surface.
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