Tag: science

Is this Philae?

9:14 am

Philae?

Cool image time! The Rosetta science team has spent much effort trying to locate Philae, which attempted to land on Comet 67P/C-G in November. The image on the right shows what they think is their best candidate, the bright feature in the center. It was not there prior to Philae’s landing attempt.

Because there are many uncertainties, however, this might not be Philae.

Ultimately, a definitive identification of this or any other candidate as being Philae will require higher-resolution imaging, in turn meaning closer flybys. This may not be possible in the near-term, as issues encountered in navigating close to the comet mean that the opportunity to make flybys at significantly less than 20 km from the surface may be on hold until later in the mission. But after the comet’s activity has subsided, Rosetta should be able to safely operate in close proximity to the comet nucleus again.

The other possibility of further refining Philae’s location would come if the lander were to receive enough power to wake-up from its hibernation and resume its scientific study of 67P/C-G. Then, CONSERT could be used to perform additional ranging measurements and significantly reduce the uncertainties on the lander’s location. At the moment, Philae is still in hibernation, but the mission team remain hopeful that, as the comet moves closer to the Sun along its orbit, the lander will receive enough power in the coming weeks or months to wake up and transmit a signal to Rosetta.

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The truth about bottled water

6:01 pm

An evening pause: Tonight’s pause is a bit different, in that it has a newsy aspect to it, illustrating the uncertainty of knowledge that makes science so difficult. It is also incredibly entertaining and funny, almost like the 1960s TV show Candid Camera. Would you be fooled like these people were?

Hat tip Phillip Oltmann.

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New close-up image of Ceres’s double bright spots

9:32 am

close-up of Ceres's bright spots

Cool image time! The Dawn science team has released a some new close-up images of Ceres, including a much higher resolution image of the dwarf planet’s double bright spot, which now resolves itself into a cluster of two larger spots with a half dozen smaller spots scattered nearby.

The region with the brightest spots is in a crater about 55 miles (90 kilometers) across. The spots consist of many individual bright points of differing sizes, with a central cluster. So far, scientists have found no obvious explanation for their observed locations or brightness levels.

“The bright spots in this configuration make Ceres unique from anything we’ve seen before in the solar system. The science team is working to understand their source. Reflection from ice is the leading candidate in my mind, but the team continues to consider alternate possibilities, such as salt. With closer views from the new orbit and multiple view angles, we soon will be better able to determine the nature of this enigmatic phenomenon,” said Chris Russell, principal investigator for the Dawn mission based at the University of California, Los Angeles.

To my eye, these bright areas resemble a wide flat caldera of a volcano. Instead of being at the top of a peak, the caldera is like a lava pool, almost like a large lake. In this case, the large spots are lakes of frozen ice that periodically melt and flow. The smaller spots are likely smaller vents where water can bubble up from below during active periods. When not active, the water will be frozen. Since ice is white and Ceres is very dark, the pools and vents appear extremely bright in these images.

I am speculating however. We will have to wait for much better images to know for sure.

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The collapse of Russian scientific innovation

9:13 am

Link here. This report documents much of what I have been seeing in the Russian space industry: an aging workforce, a lack of innovation, and concentration of power to Moscow and the central government, and an exodus of the best minds to other countries.

It appears that all of the solutions that have been imposed by Putin’s government are exactly the worst things you could do and will only make the problems grow with time.

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Finding caves on Mars

5:40 pm

A new study of pits on Mars has isolated one particular type of pit that has all the features of an Earth-like cave entrance, with a large number located in the regions around the giant volcanoes where evidence of past glacier activity has been found. From the abstract:

These Atypical Pit Craters (APCs) generally have sharp and distinct rims, vertical or overhanging walls that extend down to their floors, surface diameters of ~50–350 m, and high depth to diameter (d/D) ratios that are usually greater than 0.3 (which is an upper range value for impacts and bowl-shaped pit craters) and can exceed values of 1.8. Observations by the Mars Odyssey Thermal Emission Imaging System (THEMIS) show that APC floor temperatures are warmer at night and fluctuate with much lower diurnal amplitudes than nearby surfaces or adjacent bowl-shaped pit craters.

In other words, these pits are deeper with steeper and overhanging walls that suggest underlying passages. They also maintain warmer temperatures at night with their day/night temperatures changing far less than the surface, similar to caves on Earth where the cave temperature remains the same year-round.

The study’s most important finding, from my perspective, was the location of these pit craters.
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Did some dinosaur soft tissues survive fossilization?

2:36 pm

The uncertainty of science: New research strongly suggests that within dinosaur fossils are found many preserved soft tissues from when the creature was still living.

As early as the 1970s, researchers captured images of what looked like cellular structures inside dinosaur fossils. But did the structures contain actual tissue? Proteins commonly decay hundreds to thousands of years after an organism dies, but in rare cases they have been known to survive up to 3 million years. In a series of studies beginning a decade ago, a team led by North Carolina State University paleontologist Mary Schweitzer reported that they had extracted what appeared to be collagen, the most abundant protein in bone, from a 68-million-year-old T. rex fossil. They sequenced fragments of the protein and concluded that it closely matched that of birds, dinosaurs’ living descendants (see here and here). But other teams haven’t been able to replicate the work, and others suggested that the collagen could be contamination.

The new study, led by materials scientist Sergio Bertazzo and paleontologist Susannah Maidment, both of Imperial College London, has a different strategy for hunting down ancient proteins. Bertazzo, an expert on how living bones incorporate minerals, uses a tool called a focused ion beam to slice through samples, leaving pristine surfaces that are ideal for high-resolution imaging studies. He teamed up with Maidment to apply the technique to eight chunks of dinosaur toe, rib, hip, leg, and claw.

What they found shocked them. Imaging the fresh-cut surfaces with scanning and transmission electron microscopes, “we didn’t see bone crystallites” as expected, Maidment says. “What we saw instead was soft tissue. It was completely unexpected. My initial response was these results are not real.” [emphasis mine]

It must be noted that the new research depends on many uncertainties that still need to be replicated or confirmed.

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$28 billion spent on poor biomedical research?

2:32 pm

The uncertainty of science: A new study suggests that $28 billion is spent on biomedical research that no one can reproduce.

I have no doubt that a vast amount of medical research is so poorly done that no one else will ever be able to replicate the results. However, the article notes that the way the researchers came up with the $28 billion figure is quite questionable, reviewing only about two dozen studies and then extrapolating their numbers across the entire research field. This is highly uncertain and should be taken with a grain of salt.

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Ramp down to solar minimum continues

12:11 pm

On Sunday NOAA posted its monthly update of the solar cycle, showing the Sun’s sunspot activity in May. As I have done since 2010, I am posting it here, with annotations to give it context.

May 2015 Solar Cycle graph

The graph above has been modified to show the predictions of the solar science community. The green curves show the community’s two original predictions from April 2007, with half the scientists predicting a very strong maximum and half predicting a weak one. The red curve is their revised May 2009 prediction.

Sunspot activity once again increased in May, though it continues to remain below the 2009 prediction of activity. Though it is still early in the ramp down, a look at the present pattern suggests that (as I also noted last month) sunspot activity is declining much faster than normal. In the past, the ramp down after solar maximum was long and drawn out, while ramp up was much faster. This ramp down seems much more precipitous than past solar cycles.

I should add that in early April Sunspot Index and Long-term Solar Observations (SILSO) had declared that the peak of the solar maximum had occurred in April 2014, and that they could now sum up the overall weakness of this maximum.

Cycle 24 proves to be 30% weaker than the previous solar cycle, which reached 119.7 in July 2000, and thus belongs to the category of moderate cycles, like cycles 12 to 15, which were the norm in the late 19th and early 20th century. Compared to strong cycles, such cycles typically feature a broader maximum, with a 3-year plateau on top of which two or more surges of activity can produce sharp peaks of similar height.

I had missed this announcement when it was first posted. It is worth noting however, especially since their discussion in April is interesting to read in the context of what has happened since.

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Dawn makes a movie of Ceres

9:28 am

Cool image time! Using images that Dawn has accumulated since it entered orbit around Ceres, scientists have created an animation showing the dwarf planet as it rotates.

Video below the fold. Note that this is an animation. They have filled in the gaps between images to make the rotation smooth, exaggerated the scale two times to bring out details, and added a background of stars that is not visible in the original images. Even so, this video is scientifically useful, as it shows Ceres in its entirety. It is also very spectacular.
» Read more

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Jets on Comet 67P/C-G now persist into the night

9:18 am

jets from Comet 67P/C-G

Cool image time! Rosetta’s high resolution camera is now finding that, due to increased activity as Comet 67P/C-G approaches the sun, jets of material now continue to evaporate off the surface even after sunset.

“Only recently have we begun to observe dust jets persisting even after sunset”, says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. In the past months, the comet’s activity originated from illuminated areas on the day side. As soon as the Sun set, these jets subsided and did not re-awake until after the next sunrise. (An exception poses an image from 12 March, 2015 showing the onset of a dust jet on the brink of dawn.)

According to OSIRIS scientists, the jets now occurring even after sunset are another sign of the comet’s increasing activity. “Currently, 67P is rapidly approaching perihelion in mid-August”, says Sierks. At the time the image was taken, comet and Sun were only 270 million kilometers apart. “The solar irradiation is getting more and more intense, the illuminated surface warmer and warmer”, Sierks adds.

Because the jets are now remaining active into the night, it is allowing us to see more precisely their points of origin on the surface, which can then be studied more closely in daylight. Previously it was difficult in daylight to pinpoint the exact spot where the jets began.

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Bee die off hasn’t happened

11:39 am

The uncertainty of science: Despite numerous claims by environmentalists and scientists in the past decade that the bee population was dying off, new data from the Agriculture Department suggests that bee populations are now at a 20 year high.

The reason? It appears that beekeepers have been very innovative and creative when faced with disease or other problems that hurt bees. Driven by the profit motive and competition and free to act, they have come up with solutions.

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Hawaii’s highest court takes on TMT case

8:54 am

In a move that appears to be a victory for the protesters trying to shut down the construction of the Thirty Meter Telescope on Mauna Kea, Hawaii’s supreme court on Friday agreed to bypass lower court procedures and immediately consider the case.

It is even possible the court could rule that it is inappropriate to have any telescopes on Mauna Kea.

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Pluto’s moons rotate chaotically

12:33 pm

Data from the Hubble Space Telescope has determined that two and maybe more of Pluto’s moons have chaotic rotations.

In a surprising new study, it has been found that two of Pluto’s moons, Nix and Hydra, are in a chaotic rotation. This means that an observer on Pluto would not see the same face of the moons from one night to the next. For visitors on the moons themselves, things would get even more confusing, as every day would be a different length to the one that preceded it. The other two moons studied, Kerberos and Styx, will likely be found to be chaotic too, pending further study.

This would also mean that you would not know where on the horizon the sun or Pluto would rise each day.

This information was gathered partly to help New Horizons prepare for its July 14 fly-by.

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Astronomers accept terms imposed on them by protesters in Hawaii

5:40 pm

The University of Hawaii, which manages the astronomy operation on Mauna Kea, has accepted the terms laid down by the state’s governor for allowing construction of the Thirty Meter Telescope.

Essentially the number of telescopes on the peak will have to be reduced above and beyond the original decades-old agreement, and the University will have to find money to pay for these “native” programs:

Improved cultural research, education and training: We will work with Kahu Kū Mauna and other Native Hawaiian advisors to develop new cultural training and educational programs about Maunakea. Training is currently required for people working on the mountain and we will look for opportunities for improvement. We will develop training and education programs for visitors to ensure that all who come to Maunakea understand its cultural significance and how to respect the mountain. To ensure our cultural training and education programs are accurate, effective and continuing, we will establish at UH Hilo a new program to lead and evaluate our expanded cultural stewardship and educational activities related to Maunakea. …

New scholarship programs: The governor asked TMT to increase its support to Native Hawaiian students, particularly those from Hawaiʻi Island, who wish to pursue science and technology careers. UH recognizes its responsibilities in this area and we will launch a campaign for new scholarship programs for Hawaiʻi Island and Native Hawaiian students to increase their participation in the sciences. The university will allocate a portion of its observing time to UH Hilo for use in projects and programs to support greater participation and improved preparation of Hawaiʻi Island students for professional careers.

The first will essentially buy off the leaders of the protesters, hiring them to pound into outsiders the wonderfulness of native culture. The second, though it will provide educational scholarships — a good thing — is still essentially bigoted and discriminatory in that it determines who shall get the scholarships solely by their ethnic origin. Imagine the reaction if a university in the U.S. offered a comparable scholarship only to whites.

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Unsafe anthrax shipments more extensive than first revealed

10:37 pm

Government marches on! The Defense Department has now admitted that the improper shipment of live anthrax samples was far more widespread than they originally told us.

“As of now, 24 laboratories in 11 states and two foreign countries are believed to have received suspect samples. We continue to work closely with the Centers for Disease Control and Prevention (CDC), who is leading the ongoing investigation pursuit to its statutory authorities. The Department will continue to monitor the situation and provide updates to the public,” Defense Department said in a statement.

The Defense Department had previously reported labs in nine states and Osan Air Force Base in South Korea were impacted.

Words fail me.

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Rosetta team proposes landing on comet to finish mission

4:14 pm

Rather than simply turn off the spacecraft when its funding runs out at the end of 2015, Rosetta’s science team have proposed that the mission get a nine month extension, during which they will slowly spiral into the comet and gently land.

Their proposal is similar to what American scientists did with their NEAR spacecraft, which hadn’t been designed to land on an asteroid but was successfully eased onto the surface of Eros, where it operated for a very short time.

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Same-sex science paper retracted

9:48 am

Politics corrupts science, again: The journal Science has retracted a paper that had claimed opinions on homosexual marriage could be changed quickly during a short conversation.

As noted in the journal’s retraction statement:

The reasons for retracting the paper are as follows: (i) Survey incentives were misrepresented. To encourage participation in the survey, respondents were claimed to have been given cash payments to enroll, to refer family and friends, and to complete multiple surveys. In correspondence received from Michael J. LaCour’s attorney, he confirmed that no such payments were made. (ii) The statement on sponsorship was false. In the Report, LaCour acknowledged funding from the Williams Institute, the Ford Foundation, and the Evelyn and Walter Haas Jr. Fund. Per correspondence from LaCour’s attorney, this statement was not true.

In addition to these known problems, independent researchers have noted certain statistical irregularities in the responses. LaCour has not produced the original survey data from which someone else could independently confirm the validity of the reported findings. [emphasis mine]

LaCour was the paper’s lead author. That he cannot provide the original data immediately discredits the work. It also discredits his only co-author, Donald Green of Columbia University, who apparently put his name on the paper without ever looking at the original data as well. When the above fraud was exposed, Green quickly called for the paper’s retraction, but I wonder how it was possible he allowed it to be published in the first place. Could it have been that he supports the idea of same-sex marriage, and wanted science to contribute its support as well, regardless of the facts?

Not being able to provide the original data is the same problem that Phil Jones of the Climate Research Unit had. Jones’ work documenting the global temperature for the past century has been the main source used by the entire climate field for decades, and when he couldn’t provide his original data, saying it was lost, his work should have received the same treatment as LaCour above — immediate retraction. Instead, Science protected him, as did the entire climate community.

Their willingness to cover-up Jones’ bad science is now coming back to bite them, with more examples of sloppy work getting into publication. Jones showed that it was all right to fake his results. LaCour decided to try it as well, and Green saw no reason to challenge the dishonesty. The result? Fake science done for the sake of homosexual politics.

The big difference now, however, is the willingness of Science to quickly retract the piece. It appears we are making some progress in re-establishing the rules of science to research and publication.

A minor side note: The author of the story above is John Bohannon, the same guy who just proved you can write a fake paper and get journalists to report it.

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ALMA detects a solar flare on Mira 420 light years away

9:17 am

Mira A and Mira B

The just completed ALMA (Atacama Large Millimeter/submillimeter Array), a collection of 66 antennas located in Chile, has snapped a picture of the variable star Mira with its companion star, detecting details on the primary’s surface, including evidence of a solar flare.

Mira is a star with a mass like our Sun’s, but near the end of its life having evolved into a red giant that is shedding its outer layers. Being able to track its behavior with this kind of detail will allow astronomers to better hone their theories about the life and death of stars, including our own.

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Another major image release from Rosetta

9:34 am

Time for many cool images! The Rosetta science team has just released to the public another batch of images from its navigational camera.

The 1776 images cover the period between 23 September and 21 November 2014, corresponding to Rosetta’s close study of the comet down to distances of just 10 km from the comet centre – 8 km from the surface – and the images taken during and immediately following the landing of Philae on the comet.

You can browse through them at your leisure, making your own discoveries if you have a sharp eye and know something about planetary geology.

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A solar system like our own, but when it was a baby

9:28 am

Astronomers have discovered a very young 15 million year old star only 360 light years away that has a debris disk about the size of our solar system’s Kuiper Belt.

The ring is about the same distance from its parent star as the Kuiper belt is from the Sun, and receives roughly the same amount of light. Its blue-grey colour hints that it could consist of ices and rocky silicates such as those found in the Kuiper belt, says lead author Thayne Currie, an astronomer at the Subaru Telescope in Hawaii, which is run by the National Astronomical Observatory of Japan. “This is absolutely the closest example we have of a young Kuiper belt,” he says.

The best part of this discovery however might be how it was made, by using a new instrument on the ground-based Gemini telescope on Mauna Kea in Hawaii.

The instrument, which is part of the Gemini South telescope in Chile, uses a disk called a coronagraph to blot out the glare of bright stars. That allows it to take multi-wavelength pictures of faint, orbiting planets and debris disks around stars, by recording near-infrared light from the parent star as it scatters off the debris. The researchers discovered the disk around HD 115600 fewer than 6 months after the GPI began operation. A similar instrument, known as SPHERE, began operating in May 2014 on the European Southern Observatory’s Very Large Telescope in Chile and has also begun to make discoveries.

Assuming protesters don’t force Gemini to close, we should be getting a lot more exoplanetary discoveries from it in the coming years.

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It looks like the Moon!

9:03 am

craters on Ceres

Cool image time! Dawn has now swooped down to 3,200 miles, and provided a very nice image of the cratered surface of Ceres. Though it does appear to resemble the Moon, there are some differences that come to mind if you take a close look at the full resolution image. The surface appears smoother. All of the craters appear worn or eroded or less rugged. Also, there are no mountains. The terrain resembles the Moon’s lowlands or maria, but more so.

Note that the region in this picture is tantalizingly close to the double bright spot, but does not include it. Because Dawn is still easing its way into its first survey orbit of 2,700 miles elevation, it only takes pictures when it stops firing its ion engine, which it is doing almost all the time to get where it wants to be. Thus, they apparently only had time for this image.

The spacecraft enters its mapping orbit on June 3. Expect some cool images, including the first good images of the double bright spots, shortly thereafter.

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A journalist and filmmaking team fake a study and the press buys it

10:54 pm

The uncertainty of science journalism: How a science journalist and two documentary filmmakers fooled millions (and many science journalists) into thinking that eating chocolate will help you lose weight.

My colleagues and I recruited actual human subjects in Germany. We ran an actual clinical trial, with subjects randomly assigned to different diet regimes. And the statistically significant benefits of chocolate that we reported are based on the actual data. It was, in fact, a fairly typical study for the field of diet research. Which is to say: It was terrible science. The results are meaningless, and the health claims that the media blasted out to millions of people around the world are utterly unfounded.

He then describes step by step how they did it. They even got their “research” published in a journal that claimed it did peer review but did not change one word of their submitted manuscript and published it less than two weeks after submission and the receipt of their money (science journals traditionally require authors to pay them for the honor of publication). In the end,

We landed big fish before we even knew they were biting. Bild rushed their story out—”Those who eat chocolate stay slim!”—without contacting me at all. Soon we were in the Daily Star, the Irish Examiner, Cosmopolitan’s German website, the Times of India, both the German and Indian site of the Huffington Post, and even television news in Texas and an Australian morning talk show.

The American women’s magazine Shape also fell for the fraud.

To me, the main reason the fraud worked was because none of the journalists involved ever bothered to actually read the science paper. They saw the press release, thought the story was cool, and simply rewrote the release. This is what happens repeatedly in the science field, and is why so much crap about climate science gets published. Too many reporters accept verbatim the claims of the scientists, doing no research to check the facts on which those claims were based.

I should mention also that John Bohannon, the man who played the scientist in this prank, also ran a sting operation against peer review journals in October 2013, creating a bogus paper and getting 157 journals to accept it for publication.

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New Images of Pluto from New Horizons

5:20 pm

Pluto in mid-May

Cool image time! New images taken by New Horizons of Pluto in mid-May have begun showing faint details of the planet’s surface.

“These new images show us that Pluto’s differing faces are each distinct; likely hinting at what may be very complex surface geology or variations in surface composition from place to place,” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado. “These images also continue to support the hypothesis that Pluto has a polar cap whose extent varies with longitude; we’ll be able to make a definitive determination of the polar bright region’s iciness when we get compositional spectroscopy of that region in July.”

These images also suggest vaguely that Pluto might not be entire spherical, but I wouldn’t put much money on that speculation. We will know for sure in just a few more weeks.

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NSF to help fund the development of implantable antennas

1:47 pm

What could possibly go wrong? The National Science Foundation (NSF) is providing funding for the development of an implantable antenna for health care, including the possibility for “long-term patient monitoring.”

The project is being financed in collaboration with the National Research Foundation of Korea to create a high frequency antenna that can be permanently implanted under a person’s skin. “Antennas operating near or inside the human body are important for a number of applications, including healthcare,” a grant for the project said. “Implantable medical devices such as cardiac pacemakers and retinal implants are a growing feature of modern healthcare, and implantable antennas for these devices are necessary to monitor battery level and device health, to upload and download data used in patient monitoring, and more.”

The grant said that an implantable device could be used for “long-term patient monitoring” and “biometric tracking,” or using technology to verify a person’s identity.

Without any doubt there are many very useful applications for such an implantable device. Monitoring battery life on pacemakers is an obvious one. There will be a problem, however, if anyone but the patient can do the monitoring. I can see too many possible misuses occurring should it be in anyone else’s hands. At a minimum, there are big privacy concerns.

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Hubble films of movie of a jet firing from a black hole

12:38 pm

Cool image time! Using images taken by the Hubble Space Telescope over the past two decades astronomers have assembled a movie of the motion of blobs, ejected by a jet from a supermassive black hole at the center of a galaxy.

The jet from NGC 3862 has a string-of-pearls structure of glowing knots of material. Taking advantage of Hubble’s sharp resolution and long-term optical stability, Eileen Meyer of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, matched archival Hubble images with a new, deep image taken in 2014 to better understand jet motions. Meyer was surprised to see a fast knot with an apparent speed of seven times the speed of light catch up with the end of a slower moving, but still superluminal, knot along the string. The resulting “shock collision” caused the merging blobs to brighten significantly.

The movie is below the fold.
» Read more

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NOAA caught tampering with temperature data again

9:51 pm

A close look at NOAA’s temperature data for Maine has revealed that sometime between 2013 and 2015 the data was drastically adjusted to cool the past and warm the present.

No explanations for these changes has been offered. For some years they cooled the past as much as 4 degrees Fahrenheit, an adjustment that cannot be justified under any scientific method. As asked at the link, “Would someone please try to explain why this isn’t the biggest scandal in the history of science?”

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Drastic changes in Mars South Pole icecap

1:54 pm

Mars South Pole 2007
Mars South Pole 2015

Cool image time! Summer images taken by Mars Reconnaissance Orbiter 8 years apart of a specific area of the Martian south pole icecap show significant and surprising changes.

The top image on the right was taken August 28, 2007. The bottom image was taken March 23, 2015, four Martian years later. As noted by the science team, the bright flat-topped mesas have shrunk by about half, while the dark rough low areas have grown, eating into the mesa walls.

Closeup study of this area would provide a wealth of knowledge. It will also be very challenging, as the environment is harsh, hostile, and unstable. Imagine doing research in the Himalayas but with an unbreathable atmosphere and temperatures always far far below freezing.

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Coral islands defy sea level rise

9:39 am

The uncertainty of science: Despite having some of the highest rates of sea level rise in the past century, the 29 islands of Funafuti Atoll in the Pacific show no signs of sinking.

Despite the magnitude of this rise, no islands have been lost, the majority have enlarged, and there has been a 7.3% increase in net island area over the past century (A.D. 1897–2013). There is no evidence of heightened erosion over the past half-century as sea-level rise accelerated. Reef islands in Funafuti continually adjust their size, shape, and position in response to variations in boundary conditions, including storms, sediment supply, as well as sea level.

Be aware as well that the cause of the rise in sea level here is not clearly understood. It could be the global warming we have seen since the end of the Little Ice Age of the 1600s, or other more complex factors.

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