Space and astronomy news
Rosetta fell silent moments after 6:19 a.m. Eastern Time (12:19 UT) this morning, when it gently crashed into 67P/C-G 446 million miles (718 million km) from Earth. As the probe descended to the comet’s bouldery surface of the comet in free fall, it snapped a series of ever-more-detailed photographs while gathering the last bits data on the density and composition of cometary gases, surface temperature and gravity field before the final curtain was drawn.
Let’s take the trip down, shall we?
Rosetta awoke from a decade of deep-space hibernation in January 2014 and immediately got to work photographing, measuring and sampling comet 67P/C-G. On September 30 it will sleep again but this time for eternity. Mission controllers will direct the probe to impact the comet’s dusty-icy nucleus within 20 minutes of 10:40 Greenwich Time (6:40 a.m. EDT) that Friday morning. The high-resolution OSIRIS camera will be snapping pictures on the way down, but once impact occurs, it’s game over, lights out. Rosetta will power down and go silent.
Nearly three years have passed since Rosetta opened its eyes on 67P, this curious, bi-lobed rubber duck of a comet just 2.5 miles (4 km) across with landscapes ranging from dust dunes to craggy peaks to enigmatic ‘goosebumps’. The mission was the first to orbit a comet and dispatch a probe, Philae, to its surface. I think it’s safe to say we learned more about what makes comets tick during Rosetta’s sojourn than in any previous mission.
So why end it? One of the big reasons is power. As Rosetta races farther and farther from the Sun, less sunlight falls on its pair of 16-meter-long solar arrays. At mid-month, the probe was over 348 million miles (560 million km) from the Sun and 433 million miles (697 million km) from Earth or nearly as far as Jupiter. With Sun-to-Rosetta mileage increasing nearly 620,000 miles (1 million km) a day, weakening sunlight can’t provide the power needed to keep the instruments running.
Rosetta’s last orbits around the comet
Rosetta’s also showing signs of age after having been in the harsh environment of interplanetary space for more than 12 years, two of them next door to a dust-spitting comet. Both factors contributed to the decision to end the mission rather than put the probe back into an even longer hibernation until the comet’s next perihelion many years away.
Since August 9, Rosetta has been swinging past the comet in a series of ever-tightening loops, providing excellent opportunities for close-up science observations. On September 5, Rosetta swooped within 1.2 miles (1.9 km) of 67P/C-G’s surface. It was hoped the spacecraft would descend as low as a kilometer during one of the later orbits as scientists worked to glean as much as possible before the show ends.
The final of 15 close flyovers will be completed today (Sept. 24) after which Rosetta will be maneuvered from its current elliptical orbit onto a trajectory that will eventually take it down to the comet’s surface on Sept. 30.
The beginning of the end unfolds on the evening of the 29th when Rosetta spends 14 hours free-falling slowly towards the comet from an altitude of 12.4 miles (20 km) — about 4 miles higher than a typical commercial jet — all the while collecting measurements and photos that will be returned to Earth before impact. The last eye-popping images will be taken from a distance of just tens to a hundred meters away.
The landing will be a soft one, with the spacecraft touching down at walking speed. Like Philae before it, it will probably bounce around before settling into place. Mission control expects parts of the probe to break upon impact.
Taking into account the additional 40 minute signal travel time between Rosetta and Earth on the 30th, confirmation of impact is expected at ESA’s mission control in Darmstadt, Germany, within 20 minutes of 11:20 GMT (7:20 a.m. EDT). The times will be updated as the trajectory is refined. You can watch live coverage of Rosetta’s final hours on ESA TV .
ESAHangout: Preparing for Rosetta’s grand finale
“It’s hard to believe that Rosetta’s incredible 12.5 year odyssey is almost over, and we’re planning the final set of science operations, but we are certainly looking forward to focusing on analyzing the reams of data for many decades to come,” said Matt Taylor, ESA’s Rosetta project scientist.
Plans call for the spacecraft to impact the comet somewhere within an ellipse about 1,300 x 2,000 feet (600 x 400 meters) long on 67P’s smaller lobe in the region known as Ma’at. It’s home to several active pits more than 328 feet (100 meters) in diameter and 160-200 feet (50-60 meters) deep, where a number of the comet’s dust jets originate. The walls of the pits are lined with fascinating meter-sized lumpy structures called ‘goosebumps’, which scientists believe could be early ‘cometesimals’, the icy snowballs that stuck together to create the comet in the early days of our Solar System’s formation.
During free-fall, the spacecraft will target a point adjacent to a 425-foot (130 m) wide, well-defined pit that the mission team has informally named Deir el-Medina, after a structure with a similar appearance in an ancient Egyptian town of the same name. High resolution images should give us a spectacular view of these enigmatic bumps.
While we hate to see Rosetta’s mission end, it’s been a blast going for a 2-year-plus comet ride-along.
Breaking up isn’t hard to do if you’re a comet. They’re fragile creatures subject to splitting, cracking and vaporizing when heated by the Sun and yanked on by its powerful gravitational pull.
Recently, the Hubble Space Telescope captured one of the sharpest, most detailed observations of a comet breaking apart, which occurred 67 million miles from Earth. In a series of images taken over a three-day span in January 2016, Hubble revealed 25 building-size blocks made of a mixture of ice and dust that are drifting away from the main nucleus of the periodic comet 332P/Ikeya-Murakami at a leisurely pace, about the walking speed of an adult.
The observations suggest that the comet may be spinning so fast that material is ejected from its surface. The resulting debris is now scattered along a 3,000-mile-long trail, larger than the width of the continental U.S. Much the same happens with small asteroids, when sunlight absorbed unequally across an asteroid’s surface spins up its rotation rate, either causing it to fall apart or fling hunks of itself into space.
Being made of loosely bound frothy ice, comets may be even more volatile compared to the dense rocky composition of many asteroids. The research team suggests that sunlight heated up the comet, causing jets of gas and dust to erupt from its surface. We see this all the time in comets in dramatic images taken by the Rosetta spacecraft of Comet 67P/Churyumov-Gerasimenko. Because the nucleus is so small, these jets act like rocket engines, spinning up the comet’s rotation. The faster spin rate loosened chunks of material, which are drifting off into space.
“We know that comets sometimes disintegrate, but we don’t know much about why or how they come apart,” explained lead researcher David Jewitt of the University of California at Los Angeles. “The trouble is that it happens quickly and without warning, and so we don’t have much chance to get useful data. With Hubble’s fantastic resolution, not only do we see really tiny, faint bits of the comet, but we can watch them change from day to day. And that has allowed us to make the best measurements ever obtained on such an object.”
In the animation you can see the comet splinters brighten and fade as icy patches on their surfaces rotate in and out of sunlight. Their shapes even change! Being made of ice and crumbly as a peanut butter cookie, they continue to break apart to spawn a host of smaller cometary bits. The icy relics comprise about 4% of the parent comet and range in size from roughly 65 feet wide to 200 feet wide (20-60 meters). They are moving away from each other at a few miles per hour.
Comet 332P was slightly beyond the orbit of Mars when Hubble spotted the breakup. The surviving bright nucleus completes a rotation every 2-4 hours, about four times as fast as Comet 67P/Churyumov-Gerasimenko (a.k.a. “Rosetta’s Comet”). Standing on its surface you’d see the sun rise and set in about an hour, akin to how frequently astronauts aboard the International Space Station see sunsets and sunrises orbiting at over 17,000 mph.
Don’t jump for joy though. Since the comet’s just 1,600 feet (488 meters) across, its gravitational powers are too meek to allow visitors the freedom of hopping about lest they find themselves hovering helplessly in space above the icy nucleus.
Comet 332P was discovered in November 2010, after it surged in brightness and was spotted by two Japanese amateur astronomers, Kaoru Ikeya and Shigeki Murakami. Based on the Hubble data, the team calculated that the comet probably began shedding material between October and December 2015. From the rapid changes seen in the shards over the three days captured in the animation, they probably won’t be around for long.
Spectacular breakup of Comet 73P in 2006
More changes may be in the works. Hubble’s sharp vision also spied a chunk of material close to the comet, which may be the first salvo of another outburst. The remnant from still another flare-up, which may have occurred in 2012, is also visible. The fragment may be as large as Comet 332P, suggesting the comet split in two.
“In the past, astronomers thought that comets die when they are warmed by sunlight, causing their ices to simply vaporize away,” Jewitt said. “Either nothing would be left over or there would be a dead hulk of material where an active comet used to be. But it’s starting to look like fragmentation may be more important. In Comet 332P we may be seeing a comet fragmenting itself into oblivion.”
During its closest approach to the Sun on November 28, 2013, Comet ISON’s nucleus broke apart and soon vaporized away, leaving little more than a ghostly head and fading tail.
Astronomers using the Hubble and other telescopes have seen breakups before, most notably in April 2006 when 73P/Schwassmann-Wachmann 3, which crumbled into more than 60 pieces. Unlike 332P, the comet wasn’t observed long enough to track the evolution of the fragments, but the images are spectacular!
The researchers estimate that Comet 332P contains enough mass to endure another 25 outbursts. “If the comet has an episode every six years, the equivalent of one orbit around the sun, then it will be gone in 150 years,” Jewitt said. “It’s the blink of an eye, astronomically speaking. The trip to the inner Solar System has doomed it.”
332P/Ikeya-Murakami hails from the Kuiper Belt, a vast swarm of icy asteroids and comets beyond Neptune. Leftover building blocks from early Solar System and stuck in a deep freeze in the Kuiper Belt, you’d think they’d be left alone to live their solitary, chilly lives but no. After nearly 4.5 billion years in this icy deep freeze, chaotic gravitational perturbations from Neptune kicked Comet 332P out of the Kuiper Belt.
As the comet traveled across the solar system, it was deflected by the planets, like a ball bouncing around in a pinball machine, until Jupiter’s gravity set its current orbit. Jewitt estimates that a comet from the Kuiper Belt gets tossed into the inner solar system every 40 to 100 years.
I wish I could tell you to grab your scope for a look, but 332P is currently fainter than 15th magnitude and located in Libra low in the southwestern sky at nightfall. Hopefully, we’ll see more images in the coming weeks and months as Jewitt and the team continue to follow the evolution of its icy scraps.
The search is over, and looking at these images, no wonder it was so hard to find the little Philae lander!
The high-resolution camera on board the Rosetta spacecraft has finally spotted Philae “wedged into a dark crack on Comet 67P/Churyumov-Gerasimenko,” the ESA team said. They also said that now, seeing the lander’s orientation, it’s clear why establishing communications was so difficult following its landing on November 12, 2014.
Rosetta, orbiting the comet and getting ready for its own demise/touchdown on 67P, focused its OSIRIS narrow-angle camera towards a few candidate sites on September 2, 2016 as the orbiter came just 2.7 km of the comet’s surface. Clearly visible in the zoomed in versions are the main body of the lander, along with two of its three legs.
“With only a month left of the Rosetta mission, we are so happy to have finally imaged Philae, and to see it in such amazing detail,” says Cecilia Tubiana of the OSIRIS camera team, the first person to see the images when they were downlinked from Rosetta on September 4.
Tubiana told Universe Today via email that Philae wasn’t too hard to find in the images. “Philae was in hiding in shadow, and as soon as we stretched the brightness to ‘see’ into the shadow, Philae was there!”
She added that nothing else about Philae’s condition has been revealed from the images so far.
The Philae lander was last seen after it first touched down at a region called Agilkia on the odd-shaped, two-lobed comet 67P. During its dramatic touchdown, the lander flew, landed, bounced and then repeated that process for more than two hours across the surface, with three or maybe four touchdowns. The harpoons that were to anchor Philae to the surface failed to fire, and scientists estimated the lander may have bounced as high as 3.2 kilometers (2 miles) before becoming wedged in the shadows of a cliff on the comet. After three days, Philae’s primary battery ran out of power and the lander went into hibernation, only to wake up again and communicate briefly with Rosetta in June and July 2015 as the comet came closer to the Sun and more power was available.
But after more than a year of silence, the Rosetta team announced in mid-August 2016 that they would no longer attempt communications with Philae.
Philae’s final location had been plotted but until yesterday, never actually seen by Rosetta’s cameras. Radio ranging data was used to narrow down the search to an area spanning a few tens of meters, and a number of potential candidate objects were identified in relatively low-resolution images taken from larger distances.
Compare some of the features of the cliff in the image above to this image taken by Philae of its surroundings:
“After months of work, with the focus and the evidence pointing more and more to this lander candidate, I’m very excited and thrilled that we finally have this all-important picture of Philae sitting in Abydos,” said ESA’s Laurence O’Rourke, who has been coordinating the search efforts over the last months at ESA, with the OSIRIS and SONC/CNES teams.
At 2.7 km, the resolution of the OSIRIS narrow-angle camera is about 5 cm/pixel, which is sufficient to reveal features of Philae’s 1 m-sized body and its legs.
“This wonderful news means that we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context, now that we know where that ground actually is!” says Matt Taylor, ESA’s Rosetta project scientist.
The discovery comes less than a month before Rosetta descends to the comet’s surface. On September 30, the orbiter will be sent on a final one-way mission to investigate the comet from close up, including the open pits in a region called Ma’at, where it is hoped that critical observations will help to reveal secrets of the body’s interior structure.
“Now that the lander search is finished we feel ready for Rosetta’s landing, and look forward to capturing even closer images of Rosetta’s touchdown site,” adds Holger Sierks, principal investigator of the OSIRIS camera.
The Rosetta team said they would be providing more details about the search as well as more images in the near future.
Source: ESA
You can’t say they didn’t try, but the news is sad nonetheless. ESA announced the mission for the Philae lander – the first spacecraft to ever land on a comet — is officially over. The system that enables communications between the Rosetta spacecraft and Philae – which sitting in a shaded region on Comet 67P/Churyumov-Gerasimenko – is being switched off on July 27, 2016, at 09:00 UTC.
“It’s time for me to say goodbye,” Philae tweeted on Tuesday. “Tomorrow, the unit on @ESA_Rosetta for communication with me will be switched off forever…”
Philae has mostly been in hibernation after its dramatic touchdown (actually, three or maybe four touchdowns) on Nov. 12, 2014 when it separated from the orbiting Rosetta spacecraft, flew, landed, bounced and then repeated that process for more than two hours across the surface. The harpoons that were to anchor Philae to the surface failed to fire, and scientists estimated the lander may have bounced as high as 3.2 kilometers (2 miles) before becoming wedged in the shadows of a cliff on the odd-shaped comet. The solar-powered lander quickly ran out of power, just hours after landing. Philae’s final location has been plotted but never actually seen by Rosetta.
After months of silence, the team heard briefly from Philae on June 13, 2015, when it transmitted information on its power and computer subsystems. It then made seven intermittent contacts with Rosetta in the following weeks, with the last coming on July 9, but the communications were too short and unstable to transmit or receive any meaningful scientific or engineering data.
Since then, the Support System Processor Unit (ESS) on Rosetta was kept on in the unlikely chance that Philae would wake up and try to reestablish contact. The hope was that when the comet was closer to the Sun, it might receive enough light to power up.
But the reason for turning it off now is due to Rosetta’s own impending end of mission, coming on September 30, 2016 when it will make a controlled impact at the Ma’at region on the comet’s “head.” Emily Lakdawalla of The Planetary Society put together this annotated image of sites where Philae touched down and likely landed, and where Rosetta will end up:
The team decided to keep “Rosetta’s listening channel on until it is no longer possible due to power constraints as we move ever further from the Sun towards the end of the mission,” said Patrick Martin, ESA’s Rosetta mission manager.
Martin said that by the end of this week, the spacecraft will be about 520 million km from the Sun, and will start facing a significant loss of power – about 4W per day. In order to continue scientific operations over the next two months and to maximize their return, it became necessary to start reducing the power consumed by the non-essential payload components on board.
But, Martin added that the mission of Philae and Rosetta will always be remembered as an incredible success.
“The combined achievements of Rosetta and Philae, rendezvousing with and landing on a comet, are historic high points in space exploration,” he said.
Philae did achieve 80% of its primary science goals in its short 64-hour active mission, as it took detailed images of the comet from above and on the surface, searched for organic compounds, and profiled the local environment and surface properties of the comet, “providing revolutionary insights into this fascinating world,” ESA said.
Sources: ESA, The Planetary Society, ESA blog
Remember 252P/LINEAR? This comet appeared low in the morning sky last month and for a short time grew bright enough to see with the naked eye from a dark site. 252P swept closest to Earth on March 21, passing just 3.3 million miles away or about 14 times the distance between our planet and the moon. Since then, it’s been gradually pulling away and fading though it remains bright enough to see in small telescope during late evening hours.
While amateurs set their clocks to catch the comet before dawn, astronomers using NASA’s Hubble Space Telescope captured close-up photos of it two weeks after closest approach. The images reveal a narrow, well-defined jet of dust ejected by the comet’s fragile, icy nucleus spinning like a water jet from a rotating lawn sprinkler. These observations also represent the closest celestial object Hubble has observed other than the moon.
Sunlight warms a comet’s nucleus, vaporizing ices below the surface. In a confined space, the pressure of the vapor builds and builds until it finds a crack or weakness in the comet’s crust and blasts into space like water from a whale’s blowhole. Dust and other gases go along for the ride. Some of the dust drifts back down to coat the surface, some into space to be shaped by the pressure of sunlight into a dust tail.
You can still see 252P/LINEAR if you have a 4-inch or larger telescope. Right now it’s a little brighter than magnitude +9 as it slowly arcs along the border of Ophiuchus and Hercules. With the moon getting brighter and brighter as it fills toward full, tonight and tomorrow night will be best for viewing the comet. After that you’re best to wait till after the May 21st full moon when darkness returns to the evening sky. 252P will spend much of the next couple weeks near the 3rd magnitude star Kappa Ophiuchi, a convenient guidepost for aiming your telescope in the comet’s direction.
While you probably won’t see any jets in amateur telescopes, they’re there all the same and helped created this comet’s distinctive and large, fuzzy coma. Happy hunting!
Ready for one of the better binocular comets of 2016? Emerging from behind the Sun and a surprise outburst in January, Comet C/2013 X1 PanSTARRS is about to put on its summer show. The waning crescent Moon just crossed paths with the comet in the dawn sky on its way to New on May 6th, and the time to start tracking it is now as it plunges southward across the ecliptic this weekend. Continue reading “A Summer Comet: Our Guide to Observing X1 PanSTARRS”
Comets get blamed for everything. Pestilence in medieval Europe? Comets! Mass extinctions? Comets! Even the anomalous brightness variations in the Kepler star KIC 8462852 was blamed for a time on comets. Now it looks like the most famous maybe-ET signal ever sifted from the sky, the so-called “Wow!” signal, may also be traced to comets.
Say it ain’t so!
In August 1977, radio astronomer Jerry Ehman was looking through observation data from the Ohio State’s now-defunct Big Ear radio telescope gathered a few days earlier on August 15. He was searching for signals that stood apart from the background noise that might be broadcast by an alien civilization. Since hydrogen is the most common element in the universe and emits energy at the specific frequency of 1420 megahertz (just above the TV and cellphone bands), aliens might adopt it as the “lingua franca” of the cosmos. Scientists here on Earth concentrated radio searches at and around that frequency looking for strong signals that mimicked hydrogen.
Ehman’s searches turned up mostly background noise, but that mid-August night he spotted a surprise — a vertical column with the alphanumerical sequence “6EQUJ5″ that indicated a strong signal at hydrogen’s frequency. Exactly as predicted. Big Ear picked up the signal from near the 5th magnitude star Chi-1 Sagittarii in eastern Sagittarius not far from the globular cluster M55.
Astonished by the find, Ehman pulled out a red pen, circled the sequence and wrote a big “Wow!” in the margin. Ever since, it’s been called the Wow! signal and considered one of the few signals from space that defies explanation. Before we look at how that may change, let’s make sense of the code.
Each digit on the chart corresponded to a signal intensity from 0 to 35. Anything over “9” was represented by a letter from A to Z. It was probably the “U” that knocked Ehman’s socks off, since it indicated to a radio burst 30 times greater than the background noise of space.
In Big Ear’s 35 years of operation, it was the most intense, unexplainable signal ever recorded. What’s more, it was narrowly focused and very close to hydrogen’s special frequency.
Big Ear listened for just 72 seconds before Earth’s rotation carried the signal’s location out of “view” of antenna. Since the radio array had two feed horns, the transmission was expected to appear three minutes apart in each of the horns, but only a single one ever picked it up.
Despite follow-up observations by Ehman and others (more than 100 studies were made of the region) the signal was gone. Never heard from again. Nor has anything else like it ever been recorded anywhere else in the sky.
Careful scrutiny eliminated earthbound possibilities such as aircraft or satellites. Nor would anyone have been transmitting at 1420 MHz since it was within a protected part of the radio spectrum used by astronomers and off-limits to regular broadcasters. The nature of the signal implied a point source somewhere beyond the Earth. But where?
If it really was an attempt at alien contact, why try only once and for so short a time interval? Even Ehman doubted (and still doubts) an extraterrestrial intelligence origin, but a much more recent suggestion made by Prof. Antonio Paris of St. Petersburg College, Florida may offer an answer. Paris earlier worked as an analyst for the U.S. Department of Defense and returned to the “scene of the crime” looking for any likely suspects. After studying astronomical databases, he discovered that two faint comets, 266P/Christensen and 335P/Gibbs, discovered only within the past decade, had been plying the very area of the Wow! signal on August 15, 1977.
If you recall, a comet has two or three basic parts: a fuzzy head or coma and one or two tails streaming off behind. Invisible to earthbound telescopes, but showing clearly in orbiting telescopes able to peer into ultraviolet light, the coma is further wrapped in a huge cloud of neutral hydrogen gas.
As the Sun warms a comet’s surface, water ice or H2O vaporizes from its nucleus. Energetic solar UV light breaks down those water molecules into H2 and O. The H2 forms a huge, distended halo that can expand to many times the size of the Sun.
Paris published a paper earlier this year exploring the possibility that the hydrogen envelopes of either or both comets were responsible for the strong 1420 MHz signal snagged by Big Ear. On the surface, this makes sense, but not all astronomers agree. First off, if comets are so radio-bright in hydrogen light, why don’t radio telescopes pick them up more often? They don’t. Second, some astronomers doubt that the signals from these comets would have been strong enough to be picked up by the array.
A quick check on 266P and 335P at the time of the signal show them both around 5 a.u. from the sun (Jupiter’s distance) and extremely faint at magnitudes 22 and 27 respectively. Were they even active enough at those distances to form clouds big enough for the antenna to detect?
Paris knows there’s only one way to find out. Comet 266P/Christensen will swing through the same area again on Jan. 25, 2017, while 335P/Gibbs follows suit on January 7, 2018. Unable to use an existing radio telescope (they’re all booked up!), he’s begun a gofundme campaign to purchase and install a 3-meter radio telescope to track and analyze the spectra of these two comets. The goal is $20,000 and Paris is already well on his way there.
It would be a little bit sad if the Wow! signal turned out to be a “just a comet”, but the possibility of solving a 39-year-old mystery would ultimately be more satisfying, don’t you think?
Jupiter may be the biggest planet, but it sure seems to get picked on. On March 17, amateur astronomer Gerrit Kernbauer of Mödling, Austria, a small town just south of Vienna, was filming Jupiter through his 7.8-inch (200mm) telescope. 10 days later he returned to process the videos and discovered a bright flash of light at Jupiter’s limb.
Possible asteroid or comet impact on Jupiter on March 17
“I was observing and filming Jupiter with my Skywatcher Newton 200 telescope, writes Kernbauer. “The seeing was not the best, so I hesitated to process the videos. Nevertheless, 10 days later I looked through the videos and I found this strange light spot that appeared for less than one second on the edge of the planetary disc. Thinking back to Shoemaker-Levy 9, my only explanation for this is an asteroid or comet that enters Jupiter’s high atmosphere and burned up/explode very fast.”
The flash certainly looks genuine, plus we know this has happened at Jupiter before. Kernbauer mentions the first-ever confirmed reported comet impact that occurred in July 1994. Comet Shoemaker-Levy 9, shattered to pieces from strong tidal forces when it passed extremely close to the planet in 1992, returned two years later to collide with Jupiter — one fragment at a time. 21 separate fragments pelted the planet, leaving big, dark blotches in the cloud tops easily seen in small telescopes at the time.
Video of possible Jupiter impact flash by John McKeon on March 17, 2016
Not long after Kernbauer got the word out, a second video came to light taken by John McKeon from near Dublin, Ireland using his 11-inch (28 cm) telescope. And get this. Both videos were taken in the same time frame, making it likely they captured a genuine impact.
With the advent of cheap video cameras, amateurs have kept a close eye on the planet, hoping to catch sight of more impacts. Two factors make Jupiter a great place to look for asteroid / comet collisions. First, the planet’s strong gravitational influence is able to draw in more comets and asteroids than smaller planets. Second, its powerful gravity causes small objects to accelerate faster, increasing their impact energy.
According to Bad Astronomy blogger Phil Plait: “On average (and ignoring orbital velocity), an object will hit Jupiter with roughly five times the velocity it hits Earth, so the impact energy is 25 times as high.” Simply put, it doesn’t take something very big to create a big, bright bang when it slams into Jove’s atmosphere.
It wasn’t long before the next whacking. 15 years to be exact.
On July 19, 2009, Australian amateur Anthony Wesley was the first to record a brand new dark scar near Jupiter’s south pole using a low-light video camera on his telescope. Although no one saw or filmed the impact itself, there was no question that the brand new spot was evidence of the aftermath: NASA’s Infrared Telescope Facility at Mauna Kea picked up a bright spot at the location in infrared light.
Jupiter impact event recorded by Christopher Go on June 3, 2010
Once we started looking closely, the impacts kept coming. Wesley hit a second home run on June 3, 2010 with video of an impact flash, later confirmed on a second video made by Christopher Go. This was quickly followed by another flash filmed by Japanese amateur astronomer Masayuki Tachikawa on August 20, 2010.
Jupiter impact flash on August 20, 2010 by Masayuki Tachikawa
Prior to this month’s event, amateur Dan Petersen visually observed a impact flash lasting 1-2 seconds in his 12-inch (30.5 cm) scope on September 10, 2012, which was also confirmed on webcam by George Hall.
Keep ’em comin’!
On March 22, Comet P/2016 BA14 (Pan-STARRS) flew just 2.2 million miles (3.5 million kilometers) from Earth, making it the third closest comet ever recorded. The last time a comet appeared on our doorstep was in 1770, when Lexell’s Comet breezed by at about half that distance. Through a telescope, comet BA14 looked (and still looks) like a faint star, though time exposures reveal a short, weak tail. With an excellent map and large amateur telescope you might still find it making a bead across the Big Dipper and constellation Bootes tonight through the weekend.
Flyby Comet Imaged by Radar
While normal telescopes show few details, NASA’s Goldstone Solar System Radar in California’s Mojave Desert pinged P/2016 BA14 with radar over three nights during closest approach and created a series of crisp, detailed images from the returning echoes. They show a bigger comet than expected — about 3,000 feet (one kilometer) across — and resolve features as small as 26 feet (8 meters) across.
“The radar images show that the comet has an irregular shape: looks like a brick on one side and a pear on the other,” said Shantanu Naidu, a researcher at NASA’s Jet Propulsion Laboratory. “We can see quite a few signatures related to topographic features such as large flat regions, small concavities and ridges on the surface of the nucleus.”
I honestly thought we’d see a more irregular shape assuming that astronomers were correct in thinking that BA14 broke off from its parent 252P/LINEAR though it’s possible it happened so long ago that the “damage” has been repaired by vaporizing ice softening its contours.
Radar also shows that the comet is rotating on its axis once every 35 to 40 hours. While radar eyes focused on BA14, Vishnu Reddy, of the Planetary Science Institute, Tucson, Arizona, used the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii to examine the comet in infrared light. He discovered its dark surface reflects less than 3% of the sunlight that falls on it. The infrared data is expected to yield clues of the comet’s composition as well.
Comets are exceptionally dark objects often compared to the appearance of a fresh asphalt road or parking lot. They appear bright in photos because seen against the blackness of space, they’re still reflective enough to stand out. Comet 67P/Churyumov-Gerasimenko, still the apple of the orbiter Rosetta’s eye, is similarly dark, reflecting about 4% of sunlight.
What makes comets so dark even though they composed primarily of ice? Astronomers believe a comet grows a dark ‘skin’ both from accumulated dust and irradiation of its pristine ices by cosmic rays. Cosmic rays loosen oxygen atoms from water ice, freeing them to combine with simple carbon molecules present on comets to form larger, more complex and darker compounds resembling tars and crude oil. Dust settles on a comet’s surface after it’s set free from ice that vaporizes in sunlight.
I live in Minnesota, where our annual State Fair features every kind of deep-fried food you can imagine: deep-fried Twinkies, deep-fried fruit, deep-fried bacon and even deep-fried Smores. Just now, I can’t shake the thought that comets are just another deep-fried confection made of pristine, 4.5-billion-year-old ice toasted by eons of sunlight and cosmic bombardment.