This satellite image of the ruins of Mayapan, on Mexico's Yucatan Peninsula, hints at the apocalypse that befell a Maya kingdom hundreds of years ago.
Mayapan is considered Mexico's last Maya capital, and represents one of the largest assemblages of Maya ruins in the Yucatan. The city was built after the Maya revolted against the lords of Chichen Itza. The largest pyramid is the Castle ("El Castillo") of Kukulkan, made as a smaller replica of Chichen Itza's El Castillo pyramid. Mayapan also is home to many circular buildings, or observatories. The Maya's astronomical knowledge helped them predict the exact time of solar and planetary events and aided in the creation of precise calendars.
The city reached its zenith in the 13th century, but in the mid-1400s, factional strife led to Mayapan's decline. The rulers were killed off by a rival family during a revolt, important buildings were set ablaze, and the city was largely abandoned. By the year 1500, an epidemic drove out the stragglers. The University at Albany's Mayapan Archaeology website delves more deeply into the city's life and death.
This overhead view of Mayapan was captured by GeoEye's Ikonos satellite in 2001, from a height of 423 miles (681 kilometers). It serves as a tribute to the Maya calendar turnover on Dec. 21, as a celebration of the day's non-apocalypse — and as the latest addition to the Cosmic Log Space Advent Calendar, which has been serving up views of Earth from space on a daily basis during the holiday season. Follow the links below to catch up on the calendar's previous entries:
A vast alluvial fan blossoms across the desolate landscape between the Kunlun and Altun Mountains in western China. The river appears electric blue as it runs out of the mountains at the bottom right corner of the scene and then fans out into scores of intricate, braided channels that disappear into the desert. Dry channels — the river's former paths? — appear as silvery etchings at lower right. This scene was acquired by NASA's Terra satellite on May 2, 2002.
The geological feature spreads across the desolate landscape between the Kunlun and Altun mountain ranges that form the southern border of the Taklimakan Desert. Terra's color-coded view shows water flowing down from the mountains along the left side of the fan. Vegetation appears in shades of red in the upper left corner. NASA says the lumpy-looking terrain at the top of the image consists of sand dunes at the edge of the Taklimakan, one of the largest sandy deserts on Earth.
"Earth as Art" serves as a great kickoff for this year's Cosmic Log Space Advent Calendar, which highlights views of Earth from space. Every day from now until Dec. 25, we'll pass along a fresh image for you to enjoy. The idea takes its inspiration from a traditional Advent calendar, which lets kids count down to Christmas with a daily treat.
If one cosmic treat a day just isn't enough, you're in luck: The Hubble Space Telescope Advent Calendar has just started up over at The Atlantic's In Focus photo gallery, and Zooniverse is offering a cosmic Advent calendar as well. Feel free to fill your eyes, and your imagination, with all these non-fattening holiday goodies over the next 25 days.
The only problem with putting out a set of stamps that celebrate America's landscapes, as seen from above, is that the postage-stamp size hardly does justice to the aerial vistas. That's why we're giving you the "Earthscapes" imagery in slideshow form.
The 15-stamp set, which features pictures from aerial photographers and Earth-orbiting satellites, is available starting today from the U.S. Postal Service. The "Forever" stamps had their official unveiling at NASA's Goddard Space Flight Center in Maryland.
"Once you've seen the world from above, you never look at it quite the same way again," Joseph Corbett, the Postal Service's chief financial officer and executive vice president, was quoted as saying in a NASA news release about the kickoff. "That's why the Postal Service is proud to offer these Earthscapes stamps, which invite us to take a bird's-eye view of the land we all share."
Two of the images are from the Landsat 7 satellite, and one comes from GeoEye's Ikonos satellite. The other 12 were taken by aerial photographers. One photographer, 81-year-old Jim Wark, took five of the photos, showing Utah's Castle Butte, a railroad roundhouse in Pennsylvania, a barge operation in Houston, a skyscraper in Manhattan and a geothermal spring in Yellowstone.
The Landsat images serve as a fitting way to celebrate the 40th anniversary of the first Landsat launch. "NASA has been at the forefront of looking at Earth from the unique vantage point in space," Chris Scolese, director of Goddard Space Flight Center, said at today's ceremony. In case you're not content with just 15 pictures, here are more long-range views of Earth worth clicking through:
This half-meter resolution image shows icefields near Adelaide Island (on the west), lying at the north side of Marguerite Bay off the west coast of the Antarctic Peninsula. GeoEye tasked its GeoEye-1 satellite to collect this image on April 18.
For commercial imaging satellites, every day is Earth Day: In honor of today's eco-conscious holiday, GeoEye is releasing four recent snapshots of the planet, taken by the company's GeoEye-1 satellite as it orbited 423 miles (681 kilometers) above.
Earth Day isn't just a day for pretty pictures. It's also an occasion to reflect on the state of the planet. This picture of broken-up icefields near Adelaide Island, off the coast of the Antarctic Peninsula, is a reminder that our planet's changing climate is a continuing cause of concern. The Antarctic Peninsula is considered one of the world's fastest-warming "hotspots," as documented by imagery from Europe's Envisat satellite.
"Ice shelves are sensitive to atmospheric warming and to changes in ocean currents and temperatures," Helmut Rott, a professor from the University of Innsbruck in Austria, explained in a statement issued earlier this month. "The northern Antarctic Peninsula has been subject to atmospheric warming of about 2.5 degrees Celsius [4.5 degrees Fahrenheit] over the last 50 years —a much stronger warming trend than on global average, causing retreat and disintegration of ice shelves."
Antarctica's situation serves as a "canary in the coal mine" for the effects of global climate change and the greenhouse-gas effect, to which industrial activity is an increasing contributor. But this isn't just an issue for penguins around the South Pole, or polar bears around the North Pole. Opinion surveys indicate that the public is increasingly seeing a connection between global changes in climate and the way weather works in their own region.
For more about the Antarctic Peninsula in particular, check out this report about the effect of climate change on penguin breeding patterns, this one about concerns for seal pups, this one about the encroachment of invasive species, and this video from 2007 about the continent's shrinking "cathedral of ice." Msnbc.com's Environment section has complete coverage of today's Earth Day goings-on.
Where in the Cosmos GeoEye's picture of the Antarctic Peninsula was the subject of our latest "Where in the Cosmos" picture puzzle, posted to the Cosmic Log Facebook page. Stacy Thompson Layman was the Cosmic Log correspondent who first came up with the location shown in the picture (after a few hints), and to reward her late-night effort, I'm sending her a pair of 3-D glasses and a copy of "The World in 2050: Four Forces Shaping Civilization's Northern Future," which makes for relevant reading on Earth Day. To get in on future "Where in the Cosmos" puzzle contests, be sure to click the "like" button for Cosmic Log. Here are the three other GeoEye-1 snapshots:
GeoEye satellite image
A curl of land at the tip of Australia's Towra Point Nature Reserve, located on the southern shores of Botany Bay, looks a bit like an elephant and its trunk. A boat speeds through the bay at upper left. Situated on an ancient river delta deposit, the Towra Point reserve is designated as a wetland of international importance because it is a breeding ground and home to many vulnerable, protected or endangered species with diverse habitats. There is also a Towra Point Aquatic Nature Reserve in the surrounding waterways. GeoEye tasked its GeoEye-1 satellite to collect this image on Feb. 19.
GeoEye satellite image
This GeoEye satellite image shows a portion of the D. Ering Wildlife Sanctuary off the Siang River, directly above the Dibru-Saikhowa National Park, located about 7.5 miles (12 kilometers) north of Tinsukia, Assam, India. The sanctuary is named after the late legendary social reformer Daying Ering. The sanctuary consists of a series of islands in the Siang River that are home to endangered animals and many migratory birds. GeoEye tasked its GeoEye-1 satellite to collect this image on March 17.
GeoEye satellite image
This half-meter resolution image shows the Okavango Delta (or Okavango Swamp), located in Botswana in central southern Africa. The Okavango is the world's largest inland delta and formed where the Okavango River empties onto a swamp and into a basin in the Kalahari Desert. Most of the water is lost to evaporation and transpiration instead of draining into the sea. Botswana is one of the world's most ecologically sensitive areas. The Moremi Game Reserve spreads across the eastern side of the delta. GeoEye tasked its GeoEye-1 satellite to collect this image on April 12.
North Korea’s controversial rocket launch failed early Friday within 90 seconds of taking off.
It was an embarrassing set-back for North Korea’s new leader Kim Jong-un. But with all eyes on the reclusive country and the presence of foreign media, officials were forced to acknowledge the failure with a brief statement on state TV.
James Oberg, NBC News’s space expert and a 22-year NASA veteran, answered reader questions about the failed launch from Pyongyang earlier today.
The five-day window for the launch of a North Korean rocket mounted with an observation satellite opened Thursday as the rest of the world waits to see if Pyongyang will defy international warnings and go ahead with the controversial mission.
NBC News is in North Korea to observe the launch with space expert James Oberg. With a 22-year career as a space engineer in support of NASA’s spaceflight operations, Oberg has the experience and technical expertise to determine the veracity of North Korea’s claims about this mission.
Oberg answered reader questions for an hour earlier today. The questions and answers were extremely engaging and informative. Click below to replay the chat.
Read some of Oberg's reports on North Korea's space program:
This picture from DigitalGlobe's QuickBird satellite shows the launch pad at the Tongchang-ri Launch Facility in North Korea, as seen on April 9. Three dark-colored support vehicles are lined up on the launch apron. The rail-mounted mobile launch platform is toward the bottom of the pad, with an exhaust deflector that's designed to deal with the hot blast of launch.
While North Korean officials were showing off their preparations for a controversial satellite launch, DigitalGlobe's Quickbird satellite was snapping high-resolution pictures of the scene from far above. The images reveal how far the North Koreans have come — and how much can be gleaned about their intentions from orbit.
DigitalGlobe is a commercial satellite imagery provider, and QuickBird can provide pictures at a resolution of a half-meter (20 inches) per pixel. But you can bet that U.S. intelligence agencies are getting significantly better views of the Tongchang-ri Launch Center from their satellites.
North Korea is due to launch its Unha-3 ("Milky Way 3") rocket anytime between now and April 16, ostensibly to send an Earth-observing satellite known as Kwangmyongsong-3 ("Bright Shining Star 3") into a pole-to-pole orbit. The United States and its allies worry that the launch is really more of a test of North Korea's capability to launch intercontinental missiles as weapons.
International journalists, including a team from NBC News, were invited to visit the secretive hard-line communist nation this week for an on-the-ground assessment of the space mission. NBC News space analyst James Oberg said that in its current configuration, the booster is "not a military missile ... but it's darn close."
"This rocket is not a weapon, but it's maybe 98 percent of one," Oberg said. "It can be converted all too easily and all too frighteningly into a weapon, and they don't need it."
AmericaSpace's Craig Covault said the Tongchang-ri facility is clearly built to handle rockets much larger than the Unha-3. He quoted U.S. and South Korean intelligence analysts as saying they believe the complex could be used for tests of North Korea's "Satan" long-range ballistic missile, as well as a North Korean-Iranian booster with up to six engines clustered in the first stage.
"Iran and possibly North Korea plan to use the large new space launch booster to send Iranian and North Korean astronauts into space," Covault wrote. He lays out a Korean-Iranian missile development program that sounds positively scary.
North Korea might have been hoping that this week's visit by journalists would put Washington's fears to rest. But based on the feedback so far, it doesn't sound as if that'll be the case.
Here's tonight's report from NBC News' Richard Engel in Pyongyang:
A North Korean satellite is poised to launch to commemorate the 100th birthday of Kim Il-sung, but there are some doubts over whether it will ever go into orbit. NBC's Richard Engel reports.
... Here's a computer-generated animation of the expected launch from Analytical Graphics Inc.:
This animation from AGI shows the launch and possible path of the Unha-3 long-range rocket, aimed at putting the Kwangmongsong-3 satellite into orbit. Video courtesy of Analytical Graphics Inc. (AGI). Visit http://agi.com/northkorea for additional resources.
... And here are more satellite pictures from DigitalGlobe:
An orbital view from DigitalGlobe's QuickBird satellite shows North Korea's Tongchang-ri Launch Facility from an altitude of 420 miles (680 kilometers).
James Oberg / msnbc.com (left) / DigitalGlobe (right)
The map of the Tongchang-ri Launch Facility that was displayed by the North Koreans during a news briefing (left) is compared with the overhead view from DigitalGlobe (right). The orientation of the satellite picture has been rotated to approximate the orientation of the map.
This satellite view shows the horizontal processing building at the Tongchang-ri Launch Facility in North Korea, with a support vehicle parked in the dark-colored parking lot below the building.
This DigitalGlobe satellite image, taken from orbit on April 9, shows the Tongchang-ri Launch Facility in North Korea. The structure in the lower part of the frame is known as the high-bay processing building, and the structures in the upper pat are housing facilities. VIP housing is at leff.
When and where will Russia's doomed probe to a Martian moon fall back to Earth? The RIA-Novosti news service caused a stir when it reported that the 13-ton Phobos-Grunt spacecraft would crash in southwestern Afghanistan at 2:22 a.m. Moscow time on Jan. 14. The report attributed the prediction to the U.S. Strategic Command, but experts say it's way too early to be that precise about the Phobos-Grunt debris zone.
"Yes, it is much too early to predict" the circumstances of Phobos-Grunt's re-entry, Gene Stansbery of NASA's Orbital Debris Program Office at Johnson Space Center told me today.
The U.S. Strategic Command is being circumspect as well, deferring comment to NASA and to Roscosmos, Russia's space agency.
The most that can be said about the impact zone right now is that it will be somewhere between 51.4 degrees north and 51.4 degrees south latitude. That's a swath of the planet that stretches from Calgary, Alberta (or Ghent, Belgium) in the north to the Falkland Islands in the south and takes in the vast majority of the world's population. Satellite-watcher Marco Langbroek reports on the See-Sat-L discussion forum that the predicted time of re-entry is Jan. 13, plus or minus 11 days. A couple of weeks ago, Roscosmos estimated that re-entry would come sometime between Jan. 6 and 19.
Typically, the projected area of the debris zone can't be narrowed down until hours before re-entry, if then. It's possible that RIA-Novosti picked up on a prediction that was centered around a precise time and place of re-entry, but left out the part about the plus-or-minus uncertainty. (You can see where Phobos-Grunt is right now by checking the Heavens-Above website.)
The spacecraft was launched from Russia's Baikonur Cosmodrome in Kazakhstan on Nov. 9 local time, and was supposed to leave Earth orbit hours later for the trip to Phobos, the larger of Mars' two moons. Along the way, it would have deployed a Chinese mini-probe in Martian orbit. If everything went well, the $165 million Phobos-Grunt mission would have brought a sample of Phobos soil back to Earth in 2014. ("Phobos-Grunt," or the more correctly transliterated "Fobos-Grunt," is Russian for "Phobos-Soil.")
Everything didn't go well, as we now know: The spacecraft's upper-stage thrusters didn't fire, and it's been stuck in Earth orbit ever since. This month, Russian officials finally gave up on attempts to revive the craft and admitted that it would fall to its destruction next month.
Most of the spacecraft's mass consists of the toxic propellants it would have used to get to Phobos. There's also a small amount of radioactive cobalt-57 that was meant to power a spectrometer. The Russians say that the fuel will burn up in Earth's atmosphere, and that the cobalt won't pose a contamination threat.
Twenty to 30 parts from the probe with a total weight of up to 440 pounds (200 kilograms) are expected to survive the plunge. One of those parts could be the sample return capsule, which is designed to withstand the intense heat of atmospheric re-entry. David Warmflash, the principal investigator for one of the mission's experiments, said "it is quite possible" that his team's LIFE capsule will make it back to Earth intact.
If it lands in Afghanistan, the chances of recovery might be poor, given the proximity to a war zone. But if it lands in the ocean, which is currently the likeliest scenario, the chances aren't any better. Over the past few months, two other high-profile satellites — NASA's Upper Atmosphere Research Satellite and Germany's ROSAT space telescope — fell through the atmosphere over the South Pacific and the Bay of Bengal, respectively, and no trace of them was ever found.
This full-disk picture of Earth, provided early today by NASA, is based on archival data from imaging instruments aboard the Aqua and Terra satellites plus fresh imagery from NOAA's GOES-East weather satellite.
Woes may weigh heavy on the world at ground level, but from 22,000 miles up, even the strongest storm is a mere swirl of white on our beautiful blue planet.
This is a view of Earth on Christmas morning, blending archival imagery of Earth's surface from the MODIS instruments on NASA's Aqua and Terra satellites with hot-off-the-spacecraft weather data from NOAA's GOES-East satellite. You can see clouds streaming over the southeastern U.S. That's the storm front that brought a white Christmas to the Southwest; now it's bringing a soggy holiday to a region from Texas to Georgia. (For updates on the weather in your area and around the globe, check out msnbc.com's Weather section as well as the Weather Channel's website.)
The world looks so peaceful from orbital heights. In fact, there's a name for the positive change in perspective that comes over astronauts when they see Earth from far above: the Overview Effect. Here's how the effect is described by the Overview Institute:
"It refers to the experience of seeing firsthand the reality of the Earth in space, which is immediately understood to be a tiny, fragile ball of life, hanging in the void, shielded and nourished by a paper-thin atmosphere. From space, the astronauts tell us, national boundaries vanish, the conflicts that divide us become less important and the need to create a planetary society with the united will to protect this 'pale blue dot' becomes both obvious and imperative. Even more so, many of them tell us that from the Overview perspective, all of this seems imminently achievable, if only more people could have the experience!"
We wish you all the best for the holiday season and the new year. Here's hoping that over the past 25 days, the Cosmic Log Space Advent Calendar has given you fresh perspectives on the world, a renewed sense of wonder ... and maybe even a little taste of the Overview Effect.
We're passing along updates on the fall of NASA's Upper Atmosphere Research Satellite vla msnbc's Space section today. Because I'm traveling, that's the best place to monitor UARS' descent and re-entry, as well as the aftermath. But you know I'll be passing along nuggets of information via my Twitter account as well.
A map from Analytical Graphics Inc. shows the ground track for NASA's UARS satellite for the 28 hours from 2 a.m. ET Friday to 6 a.m. ET Saturday — which reflects The Aerospace Corp.'s estimate for the time of re-entry. During that time frame, the satellite will follow the narrow blue tracks shown on the map, but will not fly above the areas shown between the tracks.
By Alan Boyle, Science Editor, NBC News
Updated 6 p.m. ET Sept. 23:
Now that experts are narrowing down their forecasts for the fall of the six-ton Upper Atmosphere Research Satellite, you can easily work out when to look for it streaking through the sky.
Select your "current observing site" ... the easiest way to do that is to click on the "from database" link, select your country ("U" for the United States), then enter a search string for a city name (say, "Dubuque," which is where I'll be on Friday). You can also use a map, or enter in your latitude and longitude manually.
Submit your choice for observing site. That will bring you back to the home page, with your latitude/longitude listed.
Click on the link for "All Passes of UARS."
Check out the chart that comes up, and make sure the correct time zone is listed. This chart lists all the times when UARS is within the line of sight from your location. Sometimes the satellite may passing by, but you can't see it because it's lost in the daylight, or it's not reflecting any sunglint. At other times, the satellite catches the glint of the sun just right to become visible in the sky. You can get a list of those sighting opportunities by clicking the "Visible Only" button instead of the "All" button.
This chart shows UARS' sighting opportunities between now and Friday from Dubuque, Iowa.
This shows you when the UARS satellite is passing through between now and the end. But if you want to find out when there's any chance of seeing the UARS satellite fall, you have to focus on the passes that occur on Sept. 23 or early Sept. 24. For Dubuquers, there was an opportunity at 4:36 a.m. CT Sept. 24, as listed on the chart. The satellite wouldn't have been visible at that time — unless flaming pieces of debris were falling to the ground.
In that theoretical scenario, I would be watching for something streaking from west-northwest toward the south. But I wouldn't be looking very high in the sky. Heavens-Above is telling me that the maximum height above the horizon would be about 22 degrees. Ten degrees is roughly equivalent to the width of your fist held out at arm's length, so I'd look a little more than two fist-widths high.
The chart also tells me that debris from the satellite wouldn't have hit anywhere close to me, even if it was falling at the time, because the flyover is too far away. The "Alt" (altitude) listing is the key. "If your location has a pass with elevation above 80 degrees — that is, nearly overhead — then yes, you are in the potential debris scatter field," NBC News space analyst James Oberg said in an email explaining the process.
Fireworks on tap What could observers see? Space.com's skywatching columnist, Joe Rao, said the blazing re-entry would look like a "short-lived but spectacular fireworks display." At an altitude of about 50 miles (80 kilometers), chunks of the burning satelllite would break off and create a series of meteoric streaks. Large pieces would flare into fireballs that could blaze as brightly as the full moon, if the re-entry occurred at night, Rao said.
An illustration by Analytical Graphics Inc. shows the UARS satellite breaking up in the upper atmosphere.
It's far from certain that such a sight would be visible from the United States, based on NASA's estimates. The space agency said there was just a "low probability" that the satellite would be crossing North America when it made its final plunge, sometime late Friday or early Saturday.
Other experts are offering different forecasts that have been all over the map ... literally.
The Aerospace Corp.'s prediction is being updated more frequently than NASA's. At one time, it pinpointed UARS' re-entry in the south Pacific, and then the crosshairs shifted to Chad in central Africa, and then back to the Pacific. All these predictions have a wide margin of error. NASA estimates that there'll be a 6,000-mile (10,000-kilometer) margin of error even two hours in advance of the fall.
Satellite-watchers are really hoping the debris from UARS falls somewhere near them, so they can witness a spectacular sky show (and maybe even catch it on video). But others are worried about the risk of injury or damage.
NASA says the chances that anyone in particular will be hurt by UARS debris are incredibly small: A couple of weeks ago, Nicholas Johnson, head of the space agency's Orbital Debris Program Office, estimated that there's a 1-in-3,200 chance of anyone being struck by fragments. When you divide that risk among the nearly 7 billion people in a potential debris zone that stretches in latitude from northern Canada to the southern tip of South America, the risk to any particular person comes to less than 1 in 20 trillion.
NASA doesn't intend to update those odds as more becomes known about UARS' path. Those are merely the generic risk statistics for the re-entry of any space debris as big as the six-ton satellite. Johnson said one object that big comes down through the atmosphere roughly once a year. "The odds don't change," he said.
Aerospace engineers from Analytical Graphics Inc. used the company's analysis and visualization software to create this video, showing the UARS satellite in its current orbit, its potential debris area, and models for its burn-up and breakup. More info: http://blogs.agi.com
Thousands of space objects streak through the atmosphere every year: Just last week, for example, a fireball sighted over the southwestern U.S. caused a huge stir. But Oberg said the case of UARS is special because we know in advance that a fiery fall is coming.
"Unlike most rocks from space that fall on our heads, this falling satellite is known in advance, and it is that lengthy anticipation, not the inherent hazard, that makes it so newsworthy," he said. "Bigger rocks fall to Earth much faster and every day — all naturally, but out of sight, out of mind."
Aerospace engineers from Analytical Graphics Inc. used the company's analysis and visualization software to create this video, showing the UARS satellite in its current orbit, its potential debris area, and models for its burn-up and breakup. More info: http://blogs.agi.com
Update for 4:30 p.m. ET Sept. 23: NASA revised its forecast since this report was first posted to note that the Upper Atmospheric Research Satellite was not sinking as quickly as expected, and that there was a "low probability" that debris from the re-entry could fall on North America. The revised forecast said the satellite could come down late Friday or early Saturday, Eastern Daylight Time.
Earlier report from Wednesday: NASA says its derelict Upper Atmosphere Research Satellite is expected to make its final fiery plunge sometime on Friday afternoon ET and notes that "the satellite will not be passing over North America during that time period."
This afternoon's update suggests that Americans are not at any risk for injuries or property damage due to satellite debris. It also means they'll miss out on the fireworks.
For two weeks, experts on orbital debris have been telling people that the 20-year-old, bus-sized spacecraft would soon fall through the atmosphere and drop about two dozen pieces of debris on Earth — but until today, there was too much uncertainty to say exactly which day that would happen. In the morning update, NASA narrowed the time frame down to Friday. The forecast was refined further at 6:35 p.m. ET. But NASA said it couldn't yet be any more precise than to say it'll be Friday afternoon, Eastern Daylight Time.
"It is still too early to predict the time and location of re-entry with any more certainty, but predictions will become more refined in the next 24 to 48 hours," NASA said.
The six-ton satellite's orbit is limited to between 57 degrees north latitude and 57 degrees south, spanning the width of the world between northern Canada and the tip of South America. In the past, Nicholas Johnson, the head of NASA's Orbital Debris Program Office, has estimated that the chances that any of the UARS debris would hit anybody were 1 in 3,200 — which translates into a 1-in-20 trillion risk for any particular person.
NASA's Johnson told me today that he won't be recalculating the odds as the prediction becomes more precise. "At that point, we don't compute odds," he said.
NASA and its partners at the U.S. Strategic Command will be issuing updates on the timing at 24 hours before the expected fall, then at T-minus-12 hours, T-minus-6 hours and T-minus-2 hours — and we'll be passing those predictions along. But even two hours before re-entry, experts won't be able to project exactly where the debris will end up.
When UARS' predicament first came to light a couple of weeks ago, Johnson said the margin of error for the 500-mile (800-kilometer) fall zone would be somewhere around 6,000 miles, or a quarter of the way around the planet. The uncertainty arises because of a couple of factors: Solar outbursts, like the ones we've been getting over the past few weeks, lead to a faster decay of orbits for low-flying spacecraft. Also, the satellite is tumbling, which leads to unpredictable atmospheric-drag effects. Because there's no fuel left for orbital maneuvering, no one has any control over UARS' orbital course.
Most of the satellite will burn up in the atmosphere, but NASA estimates that about a half-ton's worth of fragments will survive re-entry and fall to Earth. The computer models suggest that the biggest chunk would weigh about 300 pounds (150 kilograms), or as much as a refrigerator. Anyone who happened to be in the vicinity of the debris fall would see bright streaks in the sky, much like the fireworks seen when pieces of Russia's Mir space station fell to Earth in 2001.
The most likely outcome is that the remnants of the UARS satellite would fall into a desolate patch of ocean or an uninhabited stretch of land, far away from any witnesses or potential victims. "Throughout the entire 54 years of the Space Age, there has been no confirmed report of anybody in the world being injured or severely impacted by any re-entering debris," Johnson noted two weeks ago.
A dead satellite the size of a school bus is getting lower and lower and will crash into Earth, NASA said. The best guess is that it falls on Friday. NBC's Brian Williams reports.
UARS was deployed from the shuttle Discovery in 1991, beginning a $750 million mission to study the upper atmosphere and its interaction with the solar wind. In 2005, it was shut down and placed into a disposal orbit, and its altitude has been slowly decaying ever since. Now the descent is picking up speed: NASA said its altitude at 1:30 p.m. ET today ranged from roughly 120 to 130 miles (190 to 205 kilometers).
Nowadays, satellite operators lay out a well-defined procedure for the safe disposal of Earth-orbiting satellites at the end of their lifetimes. In fact, NASA and its international partners are already devoting attention to what needs to be done when it comes time to get rid of the International Space Station, sometime after 2020. But back in the 1990s, when the UARS mission was launched, such issues were "really not given a lot of thought," Johnson said.
The circled icon on the map indicates the position of the UARS satellite at 4 p.m. ET Friday. The blue curves show its orbital track before 4 p.m., and the yellow curves show the track after 4. If UARS re-enters the atmosphere before 4, the potential fall zones include the Atlantic, Africa, Middle East, north Asia and the Pacific. If it happens after 4, South and Central America, south Asia and Australia come into the mix. But it'd be well into Friday evening by the time the orbital track goes over the U.S. and Canadian East Coast.