Drawing of the path of near-Earth asteroid 2012ge DA14 when it passes close to Earth on Feb. 15, 2013. (NASA)

Earth is about to have a close encounter with an asteroid, the nearest an object of its size has ever come to our planet.

The fly-by is expected to occur at around 1924 UTC on Feb. 15, according to scientists at NASA’s Jet Propulsion Laboratory.

The US space agency says there’s no chance the asteroid will collide with Earth.

“This is a record-setting close approach,” says Don Yeomans of NASA’s Near Earth Object Program at JPL. “Since regular sky surveys began in the 1990s, we’ve never seen an object this big get so close to Earth.”

Scientists expect the asteroid to pass us at a distance of about 27,700 km from the surface of the Earth. That’s close enough for it to pass inside the ring of a number of geosynchronous weather and communications satellites currently orbiting the Earth at about 36,000 km from Earth’s surface above the equator.

However, the asteroid should fly well above most of the satellites and spacecraft circling the planet, including the International Space Station (ISS).

To get an idea of just how close the 2012 DA14 asteroid will get to us, consider that it will come nearer to us than the moon, about 1/13th of the distance to the Moon, which is 384,400 km from Earth.

It’s expected to whiz by our planet quite fast, at a speed of about 7.8 kilometers per second in a south-to-north direction. This will be the closest an asteroid has come to Earth in at least 30 years and will give researchers a unique opportunity  to study it.

The 2012 DA14 is quite small, weighing about 130,000 metric tons and measuring about 45 meters across, less than the width of a soccer field. Astronomers believe it is made of stone, rather than metal or ice.

The asteroid was discovered by astronomers at the OAM Observatory in La Sagra, Spain less than a year ago, on Feb. 23, 2012, which is why “2012″ is part of its name.

NASA video feature of asteroid fly-by

A few other asteroids have flown even closer to Earth, but they were much smaller than the one expected to zoom by this month.  Scientists say objects of this size fly this close to the Earth about once every 40 years; an actual collision with Earth happens about every 1,200 years.

The 2012 DA14 asteroid is so tiny, it’s expected to look like a small point of light, even to those using the biggest optical telescopes. Difficult to see with the naked eye, it will be easily visible with a good set of binoculars or a small telescope.

Astronomers say the best place to see the asteroid will be in Indonesia, but people in Eastern Europe, Asia and Australia should also be able to get a glimpse.

The public can watch the event through live feeds from telescopes in La Sagra and Tenerife, Spain.

NASA astronomers at the Goldstone Deep Space Communications Complex (GDSCC) in California’s Mojave Desert will use radar imaging to determine the orbit of the asteroid, allowing them to better predict future encounters. The imaging data will also be used to create a 3D map showing the asteroid from all sides and should reveal more about the asteroid’s physical characteristics, such as its size and spin.

One out of every six stars in our Milky Way galaxy has an Earth-like planet orbiting it, according to two new studies. (Photo: Steve Jurvetson via Wikimedia Commons)

There are at least 17 billion Earth-sized worlds in our Milky Way galaxy, according to two new studies.

Both groups of scientists used data from NASA’s Kepler mission to reach their conclusions, which were presented to the American Astronomical Society in Long Beach, California.

The scientists found that the closer the planets are to their stars, the easier they are to find because they transit more frequently, giving scientists more opportunities to observe them.

One group, led by Francois Fressin of the Harvard-Smithsonian Center for Astrophysics (CfA), said its studies show 50 percent of stars in our galaxy have a planet the size of Earth or larger closely orbiting them.

Add in larger planets, which have been found to be in wider orbits around its star, and the percentage of stars with planets goes up to 70 percent, according to the researchers.

Based on current ongoing observations from the Kepler mission, along with others using different detection techniques, it looks like practically all Sun-like stars have planets, according to the Harvard-Smithsonian team.

A second group of researchers, from the University of California, Berkeley and the University of Hawaii at Manoa, found smaller exoplanets to be much more plentiful than larger ones in the star systems it observed. The analysis also confirmed that the frequency of planets increased as its size decreased, which team member Andrew Howard and the Kepler team reported last year.

Perhaps one percent of stars have planets the size of Jupiter, while 10 percent have planets the size of Neptune, according to the Berkeley/ Hawaii team. The group’s research also shows the exoplanets they observed, which were two or three times the diameter of Earth, are typically more like our solar system’s Uranus and Neptune, each of which has a rocky core  surrounded by helium and hydrogen gases and, perhaps, water.

Artist’s conception of the wide variety of planets detected by NASA’s Kepler spacecraft. (C. Pulliam & D. Aguilar/CfA)

They suggest planets orbiting close to their stars may even be water worlds, with oceans hundreds of kilometers deep, surrounding a rocky core.

Although the planets between one to two times larger than Earth may not necessarily be habitable,  the Berkeley/Hawaii team  said those planets might be rocky and, if they’re located within what they call the “Goldilocks zone” –not too hot, not too cold, just right for liquid water– could support life.

The Harvard-Smithsonian researchers found that, except for the gas giants, the type of star didn’t really have much effect on the size of its planets, contradicting previous findings. Neptune-type planets, they said, can be found just as frequently orbiting around relatively cool stars, called red dwarfs, as they are around sun-like stars. The same is true for smaller worlds.

“Earths and super-Earths aren’t picky,” said Guillermo Torres of the Harvard-Smithsonian team. “We’re finding them in all kinds of neighborhoods.”

As more data is gathered, more planets in larger orbits will be revealed, according to the Harvard-Smithsonian researchers. They say when Kepler’s mission is extended, astronomers should be able to spot Earth-sized planets at greater distances, including those with Earth-like orbits within the habitable zone.

Artist drawing of Landsat-5 in space (Image: USGS)

The longest operating Earth-observing satellite is about to be decommissioned by the US Geological Survey.

The USGS has begun the task of lowering Landsat-5 from its operational orbit.  The first series of maneuvers in that effort is likely to take place within the next month.

Landsat-5 was the fifth of seven satellites launched as part of the Landsat program, which has been acquiring satellite imagery of Earth since 1972.

Launched from California on March 1, 1984, Landsat-5 has circled Earth more than 150,000 times.

According to the USGS, which helps manage the mission, the satellite has been an extraordinary success, providing valuable contributions to the global record of land change.

Its original mission was only supposed to last three years, but Landsat-5 continued to deliver imagery and data for more than 25 more years beyond that.

The satellite experienced a number of problems over the years, but scientists and technicians managed to bring it back from the brink of failure.

This image of the abandoned city of Pripyat, home to the Chernobyl Nuclear Power Plant was taken by Landsat-5 three days after the April 26, 1986, nuclear accident. (NASA)

However, the recent failure of one of its gyroscopes proved to be one problem too many, finally bringing Landsat-5′s decades-long mission to an end.

“This is the end of an era for a remarkable satellite, and the fact that it flew for almost three decades is a testament to the NASA engineers and the USGS team who launched it and kept it flying well beyond its expected lifetime,” said Anne Castle, Department of the Interior assistant secretary for Water and Science. “The Landsat program is the gold standard of satellite observation, providing an invaluable public record of our planet that helps us tackle critical land, water, and environmental issues.”

Over more than a quarter of a century, Landsat-5  observed and sent back Earth imagery and data  reflecting the many changes which have taken place on our planet, not only from natural hazards and a changing climate, but also due to land use practices.

It observed the eruption of Mount Saint Helens, the 1991 Kuwaiti oil fires set by a fleeing Iraqi military, the 1986 Chernobyl nuclear disaster, as well as rainforest depletion, wildfires, floods, global crop production, and the expansion and retreat of the Earth’s ice shelves.

Image taken by Landsat-5 in 1991 shows inky-black smoke pouring from burning oil wells which were set afire by defeated Iraqi military forces as they retreated from Kuwait. (NASA)

“Any major event since 1984 that left a mark on this Earth larger than a football field was likely recorded by Landsat-5, whether it was a hurricane, a tsunami, a wildfire, deforestation, or an oil spill,” said USGS Director Marcia McNutt. “We look forward to a long and productive continuation of the Landsat program, but it is unlikely there will ever be another satellite that matches the outstanding longevity of Landsat-5.”

Landsat-5 observations have helped increase our understanding and awareness of the impact humans have on the land, according to the USGS.

With Landsat-5 out of commission, a number of Earth-observing satellites put into space by other governments and private companies, continue to operate.

Landsat-7, which launched in 1999, and the upcoming  Landsat-8 (LDCM), which launches in 2013, will take up where Landsat-5 left off, continuing to keep watch over an ever-changing planet.

NASA finds there are more potentially hazardous asteroids (PHA)s, closely aligned with the plane of our solar system than previous models suggested. (Image: NASA/JPL-Caltech)

First, the good news. There are fewer asteroids near Earth than previously estimated.  Now the bad news. A new NASA survey also finds there may be more than twice as many aligned with Earth’s orbit than thought, which could increase the odds of an asteroid coming close enough to us to cause concern.

The findings from NASA/JPL’s Near Earth Object Wide-field Infrared Explorer (NEOWISE) project also reveal new information about the origins and possible dangers these space objects might pose.

Potentially hazardous asteroids, or PHA’s, are a subset of a larger group of near-Earth asteroids,  which come within eight million kilometers of us and are big enough to pass through Earth’s atmosphere, causing a great amount of damage.

To get a count on how many of these possible troublemakers are out there, NASA used one of its space telescopes to make an assessment of our solar system’s population of PHA’s.

WISE, an unmanned satellite carrying an infrared heat-sensitive telescope, was launched in December 2009 and spent a little over a year imaging the entire sky to provide data on asteroids, the coolest and dimmest stars, and the most radiant galaxies.

Approximately 4,700 PHAs, give or take about 1,500, with diameters larger than 100 meters, were found, according to NEOWISE principal investigator Amy Mainzer.

Most of the asteroids in our solar system never get close to Earth.  They’re found in what’s called the Asteroid Belt, which is between the orbits of Mars and Jupiter.

Scientists think these asteroids may have been fragments that were trying to come together to form a planet when the solar system was forming.  However,  the overwhelming gravitational influence of Jupiter was so strong, it kept the planet from forming.

But, occasionally, if there is an interaction with one of the giant planets, some of the asteroids may be forced to wander away from the main belt and into near-Earth space – causing concern for those of here on terra firma.

To make their tally, Mainzer along with her colleagues at JPL examined approximately 107 PHA’s with WISE telescope data, providing them with a representative sample of the total population of these potentially dangerous objects.

From that sample, Mainzer’s team was able to calculate the total number of PHA’s in the solar system.

This diagram illustrates the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid (PHA) (orange). (Image: NASA/JPL-Caltech)

Of course, the big question remains how likely is it that one of these potentially-hazardous asteroids actually could strike Earth.   Mainzer, looking back at Earth’s history, points out that major asteroid strikes very rarely happen.  Scientists estimate that such a major hit happens every 100 million years or so.  The last mammoth asteroid collided with Earth about 65 million years ago, causing, scientists think, the extinction of most life on our planet, including the dinosaurs.

Mainzer says astronomers have already discovered most of the significant asteroids out there.  However, she warns, there are many smaller asteroids, which haven’t been discovered yet.  The NEOWISE study indicates that only between 20 and 30 percent of these have been discovered so far.

To keep us safer from asteroid impacts, Mainzer says the most important thing that we can do is actually go look for them.  “Because, if you don’t know where they are, you have no idea how to really deal with any risk,” she says.

Mainzer and her colleagues are currently working on a proposal to build and carry out an advanced survey mission.  Called the Near Earth Object Camera (NEOCam), this proposed mission would locate many more asteroids to provide a more accurate picture of the total asteroid population.

Dr. Amy Mainzer joins us on this week’s radio edition of Science World.  Check out the right column for scheduled air-times or listen to the interview with Dr. Mainzer below.

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Other stories we cover on the “Science World” radio program this week include:

• Success! Privately-funded cargo spacecraft docks with the ISS
• Recommendation to halt prostate cancer screening stirs controversy
• Scientists, lawmakers target invasive Asian fish species
• Babies born by C-section more likely to become obese, study says