Tag: science

Escape velocity on Phobos changes a lot depending on location

9:34 am

A new computer analysis of the shape of the gravitational field of the Martian moon Phobos suggests that the escape velocity varies significantly, depending on where you are on the moon’s surface.

Phobos is an odd duck among our solar system’s moons. It’s tiny (a fraction of a percent the size of our own moon) and is shaped like a potato; that weird shape draws gravity to different places, depending on where you are.

All these features make Phobos a challenge to travel on, researchers report in Advances in Space Research. In some places, moving any faster than 5 kilometers per hour would be enough to free you from the moon’s meager gravitational pull, sending you off into space where you’d likely be captured by Mars’s gravity and end up orbiting the Red Planet. The fastest you could travel anywhere on Phobos would be about 36 kilometers per hour, or a little faster than a golf cart, the team finds.

Obviously, this must be recognized for any mission trying to land and explore the moon.

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Astronomers identify first progenitor star for Type 1C supernovae

3:27 pm

Astronomers have for the first time identified a progenitor star for a Type 1C supernovae.

[The search for supernovae progenitor stars has found] a few pre-supernova stars. But the doomed stars for one class of supernova have eluded discovery: the hefty stars that explode as Type Ic supernovas. These stars, weighing more than 30 times our Sun’s mass, lose their hydrogen and helium layers before their cataclysmic death. Researchers thought they should be easy to find because they are big and bright. However, they have come up empty. Finally, in 2017, astronomers got lucky. A nearby star ended its life as a Type Ic supernova. Two teams of researchers pored through the archive of Hubble images to uncover the putative precursor star in pre-explosion photos taken in 2007. The supernova, catalogued as SN 2017ein, appeared near the center of the nearby spiral galaxy NGC 3938, located roughly 65 million light-years away.

An analysis of the candidate star’s colors shows that it is blue and extremely hot. Based on that assessment, both teams suggest two possibilities for the source’s identity. The progenitor could be a single star between 45 and 55 times more massive than our Sun. Another idea is that it could have been a binary-star system in which one of the stars weighs between 60 and 80 times our Sun’s mass and the other roughly 48 solar masses. In this latter scenario, the stars are orbiting closely and interact with each other. The more massive star is stripped of its hydrogen and helium layers by the close companion, and eventually explodes as a supernova.

As can be seen by the quote above, identifying the star that exploded still leaves much unknown, including whether the star is a single or a binary. Still, they finally have some idea what kind of star erupts in a Type IIC supernovae, which will help constrain the theories for explaining the cause of these explosions.

Note also that this identification will not be confirmed until the supernova itself completely fades in about two years. They might find when that happens that the candidate progenitor is still there, meaning it was not the progenitor of the supernova at all.

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Scientists admit to many errors in ocean warming paper

2:45 pm

The uncertainty of science: The scientists who wrote a much heralded paper a few weeks ago claiming that the oceans are retaining far more heat than previously believed have admitted that their paper has many errors that make its conclusions far more uncertain.

Scientists behind a major study that claimed the Earth’s oceans are warming faster than previously thought now say their work contained inadvertent errors that made their conclusions seem more certain than they actually are.

Two weeks after the high-profile study was published in the journal Nature, its authors have submitted corrections to the publication. The Scripps Institution of Oceanography, home to several of the researchers involved, also noted the problems in the scientists’ work and corrected a news release on its website, which previously had asserted that the study detailed how the Earth’s oceans “have absorbed 60 percent more heat than previously thought.”

“Unfortunately, we made mistakes here,” said Ralph Keeling, a climate scientist at Scripps, who was a co-author of the study. “I think the main lesson is that you work as fast as you can to fix mistakes when you find them.”

The central problem, according to Keeling, came in how the researchers dealt with the uncertainty in their measurements. As a result, the findings suffer from too much doubt to definitively support the paper’s conclusion about how much heat the oceans have absorbed over time. [emphasis mine]

To put it more bluntly, their conclusions are worthless, the data being too uncertain.

When this paper came out two weeks ago I looked at it, and found myself questioning its results. They seemed too certain. Moreover, their work was too perfect for confirming the theory that the oceans are retaining more heat and thus causing the pause in global warming that no global warming model predicted. It fit the model of most climate research these days, unreliable and unconvincing, which is why I did not post it on Behind the Black.

Now, only two weeks later, we find the researchers backing off from their certain conclusions. If anything is a perfect demonstration of confirmation bias, this story is it. These global warming scientists want desperately to prove their theories, and since their models haven’t been working they are desperately searching everywhere they can for explanations. In this case that search led them astray.

The truth is that maybe the climate field should take a step back and reconsider its entire assumptions about carbon dioxide and global warming. They might actually end up doing better science, and thus do a better job at getting us closer to the truth.

A side note: That this paper passed peer review, and was strongly touted by the media and the science community, illustrates once again how much that media and science community has allowed its biases to cloud its vision. This paper should never have been published with these errors. Period.

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Scientists discover giant impact crater buried under Greenland ice

2:34 pm

Scientists have discovered the existence of a giant impact crater buried under the Greenland ice.

An international team of researchers, including a NASA glaciologist, has discovered a large meteorite impact crater hiding beneath more than a half-mile of ice in northwest Greenland. The crater — the first of any size found under the Greenland ice sheet — is one of the 25 largest impact craters on Earth, measuring roughly 1,000 feet deep and more than 19 miles in diameter, an area slightly larger than that inside Washington’s Capital Beltway.

They think, based on the data, that this crater is very young, one of the youngest known on Earth. At the most is is no more than 3 million years old.

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Null result from Spitzer suggests Oumuamua was small

1:43 pm

The uncertainty of science: The inability of the infrared Spitzer Space Telescope to detect the interstellar object Oumuamua as it exited the solar system suggests the object is small.

The fact that ‘Oumuamua was too faint for Spitzer to detect sets a limit on the object’s total surface area. However, since the non-detection can’t be used to infer shape, the size limits are presented as what ‘Oumuamua’s diameter would be if it were spherical. Using three separate models that make slightly different assumptions about the object’s composition, Spitzer’s non-detection limited ‘Oumuamua’s “spherical diameter” to 1,440 feet (440 meters), 460 feet (140 meters) or perhaps as little as 320 feet (100 meters). The wide range of results stems from the assumptions about ‘Oumuamua’s composition, which influences how visible (or faint) it would appear to Spitzer were it a particular size.

The new study also suggests that ‘Oumuamua may be up to 10 times more reflective than the comets that reside in our solar system – a surprising result, according to the paper’s authors.

These results fit the models that explain Oumuamua’s fluctuations in speed as caused by the out gassing of material, like a comet. They also do not contradict the recent hypothesis that the object might have been an alien-built light sail.

The simple fact is that we do not have enough data to confirm any of these theories.

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Volcanic rivers on Mars

12:53 pm

Granicus Valles

Cool image time! The photo on the right, cropped and reduced to post here, was part of the November image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO). If you click on the image you can see the full resolution picture.

The uncaptioned release webpage is dubbed “Faults in Granicus Valles.” The image itself only shows a small part of Granicus Valles, named after a river in Turkey, that flows down from the estern slopes of the giant volcano Elysium Mons. While far smaller than the four big Martian volcanoes in the Tharsis region to the east and near Marines Valles (which I highlight often), Elysium Mons still outshines anything on Earth at a height of almost 30,000 feet and a width of 150 miles. It sits at about the same northern latitude of Olympus Mons, but all by itself, rising up at the very northern edge of the transition zone between the southern highlands and the northern plains, with the vast Utopia Basin, the second deepest basin on Mars, to the west.

Overview of Elysium Mons and Granicus Valles

Granicus Valles itself is almost five hundred miles long. At its beginning it flows in a single straight fault, but once it enters the northern plains of Utopia Basin it begins to meander and break up into multiple tributaries. The MRO image above shows only a tiny portion in the northern plains, as illustrated by the white box in the overview map to the left.
» Read more

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SuperEarth orbiting Barnard’s Star?

11:18 am

The uncertainty of science: Astronomers have discovered a candidate exoplanet orbiting Barnard’s Star, the closest single star to our solar system and the second closest stellar system after Alpha Centauri.

The planet candidate, named Barnard’s star b (or GJ 699 b), is a super-Earth with a minimum of 3.2 Earth masses. It orbits its cool red parent star every 233 days near the snow-line, a distance where water would be frozen. In the absence of an atmosphere, its temperature is likely to be about -150 ºC, which makes it unlikely that the planet can sustain liquid water on its surface. However, its characteristics make it an excellent target for direct imaging using the next generation of instruments such as NASA’s Wide Field InfraRed Survey Telescope (WFIRST, [3]), and maybe with observations from the ESA mission Gaia [4].

The reason I put a question mark in the headline is that this is not the first time a candidate exoplanet has been proposed to orbit Barnard’s Star. In the 1960s astronomer Peter van de Kemp claimed the star had at least one gas giant orbiting it every 24 years. It was later found that the periodic motion variations he measured were due to “to an artifact of maintenance and upgrade work” at the telescope he was using.

The result above has not been confirmed by other means, so they must list this superEarth as a candidate exoplanet. More observations are necessary to confirm it.

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Neutron star merger caused gravitational wave?

10:17 am

The uncertainty of science: Astronomers now believe that one of the half dozen or so gravitational waves detected by LIGO was likely caused by the merger of two neutron stars.

One of these, GW170817, resulted from the merger of two stellar remnants known as neutron stars. These objects form after stars much more massive than the Sun explode as supernovae, leaving behind a core of material packed to extraordinary densities.

At the same time as the burst of gravitational waves from the merger, observatories detected emission in gamma rays, X-rays, ultraviolet, visible light, infrared and radio waves – an unprecedented observing campaign that confirmed the location and nature of the source.

The initial observations of GW170817 suggested that the two neutron stars merged into a black hole, an object with a gravitational field so powerful that not even light can travel quickly enough to escape its grasp.

While intriguing, this result is uncertain, and based on many assumptions.

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Powerful 1972 solar storm detonated ocean mines in Vietnam

10:12 am

Scientists studying a powerful 1972 storm have also uncovered a recently released Navy report that showed the storm was powerful enough that it detonated ocean mines off the coast of Vietnam.

On the same day [the storm arrived on Earth], while observing the coastal waters of North Vietnam from aircraft, US Navy personnel witnessed dozens of destructor sea mines exploding with no obvious cause. These mines were airdropped by the US Navy into Vietnamese waters as part of Operation Pocket Money, a mission aimed at blocking supplies from reaching North Vietnamese ports.

The Navy promptly investigated the peculiar explosions, working with the National Academy of Sciences and the National Oceanic and Atmospheric Administration, to conclude that more than 4,000 mine detonations were most likely triggered by the solar storm, Knipp said.

A now declassified report about the mining of North Vietnam from the Chief of Naval Operations at the Mine Warfare Project Office noted, “this was the first example of what happens to a major mining campaign in the face of the vagaries of nature.”

Many of the destructor mines were designed to trigger if they sensed changes in magnetic fields associated with moving ships. Solar activity is known to perturb Earth’s magnetic field, and in early August 1972, the perturbations were likely strong enough to meet the magnetic requirements for detonation, Knipp said.

This proves once again that one must not dismiss any possibility in trying to understand what happens in the universe. Don’t be credulous, but don’t be close-minded either. The universe can surprise you.

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LSST’s giant coating chamber arrives in Chile

2:54 pm

The giant coating chamber that will be used to coat the mirrors for the Large Synoptic Survey Telescope has arrived in Chile.

The Coating Chamber and its associated equipment will share this level with the camera maintenance rooms, the vertical platform lift, and the shipping and receiving area. The Coating Chamber will be used to coat LSST’s mirrors when they arrive on Cerro Pachón, and to re-coat the mirrors periodically during Operations.

LSST will conduct a 10-year survey, and during this period its mirrors will be exposed to the elements each night as the telescope surveys the sky through the open side of the observatory dome. Over time the mirrors will get dusty, and the mirror coatings may develop small blemishes that eventually affect the telescope’s performance. To ensure that LSST continues to collect the sharpest possible images of the night sky, its mirrors will undergo periodic washing and recoating. It’s anticipated that the Primary/Tertiary Mirror (M1M3) will need to be recoated every two years, and the Secondary Mirror (M2) every five years, during the 10-year survey. Both the washing and recoating will be done inside the observatory; special equipment will be used to remove and transport the mirrors from the telescope to the washing station and coating chamber.

LSST will essentially be imaging the entire visible sky nightly, making it possible over time to track sudden events, such as supernovae, as they happen.

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Evidence of nitrogen ice glaciers on Pluto

2:49 pm

Using data sent back by New Horizons during its fly-by of Pluto scientists now think they have identified land forms created by past nitrogen ice glaciers.

The washboard and fluted terrain … occur at the location on Sputnik Planitia’s perimeter where elevations and slopes leading into the surrounding uplands are lowest, and also where a major tectonic system coincides with the edge of Sputnik Planitia. The low elevation of the area makes it a natural setting for past coverage by nitrogen ice glaciers, as indicated by modeling of volatile behavior on Pluto performed by Dr. Bertrand at Ames.

Through comparison of the washboard and fluted texture with parallel chains of elongated sublimation pits (depressions in the surface formed where ice turns directly into a gas) seen in southern Sputnik Planitia, the ridges are interpreted to represent water ice debris liberated by tectonism of underlying crust. This water ice debris was buoyant in the denser, pitted glacial nitrogen ice that is interpreted to have formerly covered this area, and collected on the floors of the elongated pits. After the nitrogen ice receded via sublimation, the debris was left as the aligned ridges, mimicking the sublimation texture – washboard ridges where deposited on flat terrain, and fluted ridges where deposited on steeper slopes.

This is strange stuff. The solid bedrock here, water ice, will float on the nitrogen ice sitting on top of it. Thus, the material that wants to sublimate away, nitrogen, sometimes has to fight its way past the water ice that has risen to the top of the pile.

To put it mildly, we hardly understand these alien processes. This research is merely a first stab, the first hand-waving.

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Earth’s atmosphere cooling as solar minimum arrives

8:59 am

The uncertainty of science: With the early arrival of the solar minimum, the Earth’s atmosphere has quickly shown signs of cooling.

New research shows that Earth’s upper atmosphere is responding. “We see a cooling trend,” says Martin Mlynczak of NASA’s Langley Research Center. “High above Earth’s surface, near the edge of space, our atmosphere is losing heat energy. If current trends continue, it could soon set a Space Age record for cold.”

These results come from the SABER instrument onboard NASA’s TIMED satellite. SABER monitors infrared emissions from carbon dioxide (CO2) and nitric oxide (NO), two substances that play a key role in the energy balance of air 100 to 300 kilometers above our planet’s surface. By measuring the infrared glow of these molecules, SABER can assess the thermal state of gas at the very top of the atmosphere–a layer researchers call “the thermosphere.”

“The thermosphere always cools off during Solar Minimum. It’s one of the most important ways the solar cycle affects our planet,” explains Mlynczak, who is the associate principal investigator for SABER.

What effect this upper atmosphere cooling will have on the surface climate is somewhat uncertain, though there is a great deal of evidence suggesting the surface climate will cool also.

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More Pits on Mars!

3:30 pm

Pits near Arsia Mons

Cool image time! In the November image release from the high resolution camera on Mars Reconnaissance Orbiter (MRO) were three images, dubbed by me in the collage above as number one, number two, and number three, showing pits south of Arsia Mons, the southernmost volcano in the chain of three giant volcanoes to the east of Mars’s largest volcano, Olympus Mons, and to the west of the Marineris Valles valley.

Mars overview showing pit locations

The image on the right provides the geographical context of the three pits. They are all south of the volcano on the vast lava flow plains that surround it. The location of pits #1 and #2 is especially intriguing, on the east and west edges of what appears to be a large lava flow that had burst out from the volcano, leaving a large lava field covering a vast area several hundred miles across just to the south. You can also see a similar large lava field to the north of the volcano. Both fields appear to have been formed when lava poured through the breaks created by the fault that cuts through the volcano from the northeast to the southwest.
» Read more

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The ExoMars 2020 landing site

10:23 am

ExoMars 2020 landing site

Last week the European Space Agency (ESA) announced the final chosen landing site for their 2020 ExoMars rover, a region called Oxia Planum.

Since then they have posted several detailed overview maps describing this region. The image on the right, reduced slightly to post here, shows the final two candidate elliptical landing sites in black, with Oxia Planum on the left. The caption for this image adds this tantalizing detail:

Both landing site candidates lie close to the transition between the cratered northern highlands and the southern lowlands of Mars. They lie just north of the equator, in a region with many channels cutting through from the southern highlands to the northern lowlands. As such, they preserve a rich record of geological history from the planet’s wetter past, billions of years ago.

To understand better what they mean by this, we need to zoom out.
» Read more

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Jupiter’s upper clouds

9:02 am

Jupiter's upper clouds

Cool image time! The photograph on the right, reduced to post here, was created by citizen scientists Gerald Eichstädt and Seán Doran from the raw images taken by Juno during the spacecraft’s 16th close fly-by of Jupiter on October 29, 2018. If you click on it you can see the full resolution image.

At the time, Juno was about 4,400 miles (7,000 kilometers) from the planet’s cloud tops, at a latitude of approximately 40 degrees north.

What attracts me to this image is its dimensionality. First, it looks at Jupiter from an oblique angle. Second, the shadows of the upper clouds can clearly be seen being cast on the lower clouds. Third, if you look at the full resolution image you can even see this effect in the middle of the big white storm in the image’s top left.

What frustrates me about this image is that Juno is not in an orbit around Jupiter allowing it to make extended movies of the evolution of these cloud features. Gaining even a limited understanding the meteorology of this gas giant will simply not be possible until we can do this, and that will require many satellites orbiting the planet.

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Europe picks landing site for its ExoMars 2020 rover

4:32 pm

The European Space Agency (ESA) has chosen the landing site for its ExoMars 2020 rover, a generally flat area with scattered craters dubbed Oxia Palum.

After over 4 years of careful study of HiRISE and more recently CaSSIS images Oxia Planum was chosen because scientists were convinced that its fine grained sediments, deposited during the ancient Noachian epoch were ideally suited for the Exobiology rover. With an enormous catchment area the sediments will have captured organics from a wide variety of environments over a long period of time, including areas where life may have existed. The fine sediments should also be ideal for the ExoMars drill – it aims to get to 2 metres depth.

Remote identification with the Mars Express and Mars Reconnaissance Orbiter Infrared spectrometers shows the presence of clays and other minerals giving clues to its aqueous history. A large group of scientists have been working on proposing, characterising and down selecting the sites, all of which had fascinating aspects, but Oxia Planum is the clear winner on both science and engineering constraints.

Based on my analysis of the last two candidate sites, I would guess that they also picked Oxia Planum because it is less spectacular, flatter, and thus poses less risk. It also means the images from there will be a bit more boring for the ordinary person.

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Mars rover update: November 8, 2018

10:08 am

Summary: Curiosity finally gets drill samples from the top of Vera Rubin Ridge. Opportunity’s silence now extends to five months.

For a list of past updates beginning in July 2016, see my February 8, 2018 update.

Curiosity

Curiosity's travels on and off Vera Rubin Ridge

For the overall context of Curiosity’s travels, see Pinpointing Curiosity’s location in Gale Crater.

The traverse map on the right, unchanged from my last rover update on July 17, 2018, shows almost all of Curiosity’s travels on Vera Rubin Ridge. The yellow dotted line is the oldest travel, up onto the ridge and then back down to get a successful drill sample. The green dotted line shows the rover’s return back up onto the top of the ridge, where it attempted and failed to drill into the ridge’s top layer, then experienced a serious computer issue in mid-September that essentially shut down science operations for about five weeks.

With the resumption of science operations about two weeks ago, the rover has moved a short distance on the top of the ridge to a new drill location, where it finally succeeded this week in drilling a hole in the hardest top layer of Vera Rubin Ridge.
» Read more

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Parker survives first close solar fly-by

4:05 pm

The Parker Solar Probe has successfully survived its first close fly-by of the Sun.

Mission controllers at the Johns Hopkins University Applied Physics Lab received the status beacon from the spacecraft at 4:46 p.m. EST on Nov. 7, 2018. The beacon indicates status “A” — the best of all four possible status signals, meaning that Parker Solar Probe is operating well with all instruments running and collecting science data and, if there were any minor issues, they were resolved autonomously by the spacecraft.

At its closest approach on Nov. 5, called perihelion, Parker Solar Probe reached a top speed of 213,200 miles per hour, setting a new record for spacecraft speed. Along with new records for the closest approach to the Sun, Parker Solar Probe will repeatedly break its own speed record as its orbit draws closer to the star and the spacecraft travels faster and faster at perihelion.

It will be several weeks before they can download all the data gathered during this first fly-by.

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Puzzling fractures on Mars

11:31 am

Fractures on Mars

Cool image time! Today the Mars Reconnaissance Orbiter (MRO) science team released another month’s worth of images from the spacecraft’s high resolution camera. The picture on the right, reduced in resolution to post here, was the first image that I took a close look at, and decided it was worth posting immediately. If you click on the image you can see the full resolution version.

This image lacks a caption, but the release webpage is titled “Fractured Crater Floor.” It shows several cross-crossing fissures, some wide enough for dust to gather within into sand dunes. The fractures themselves appear to be cutting across a bulging dome.

My first reaction was to wonder where the heck this crater was on Mars, how big was it, and how dominate were the fractures within its floor. The image itself does not answer any of these questions. The fractures could be filling the floor, or not, and the crater could be small or big. Moreover, its location might help explain the cause of the fractures.

To understand any of the images from MRO it is always important to zoom out to get some context.
» Read more

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Bennu’s two hemispheres

9:05 am

Bennu's two hemispheres

The image above of the two hemispheres of the asteroid Bennu, cropped and reduced very slightly to post here, was created from several images taken by OSIRIS-REx on two different days last week.

These two super-resolution views of asteroid Bennu were created using eight 2.5-millisecond exposure images captured by OSIRIS-REx on two separate days. The view on the left is composed of eight PolyCam images taken over the span of two minutes on Nov. 1, 2018, when the spacecraft was about 126 miles (203 km) from the asteroid. The one on the right – showing the opposite side of the asteroid – was generated using eight images taken during the same two-minute time slot on Nov. 2, from a distance of about 122 miles (196 km).

The rock on the southern limb is the same in both images, merely seen from opposite sides. Bennu appears very similar to Ryugu, except that there do appear to be dark areas on its surface, possibly crater sites, that might be smooth enough for landing.

The rendezvous at Bennu will occur on December 3.

UPDATE: The OSIRIS-REx science team has now released a short movie showing Bennu’s rotation as imaged during this same time period.

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China still struggling to find scientists to run FAST radio telescope

8:32 am

China is still finding it difficult to hire the scientists necessary to run its FAST radio telescope, the largest single dish radio telescope in the world.

And why is that?

For job candidates, the major stumbling blocks often are financial incentives and research independence, researchers told the South China Morning Post. The telescope’s remote location also may give candidates pause.

George Smoot, a Hong Kong University of Science and Technology professor who won the Nobel Prize in physics in 2006, said candidates interested in working in a more developed setting might think twice about spending a lot of time in an area known for its traditional rural villages.

“Another issue is how much the Chinese Academy of Sciences will influence and direct activities there,” Smoot said. “It is an issue to people unless they have some straight link.” [emphasis mine]

It must always be remembered that nothing in China is done without the government’s approval. For western astronomers, used to having a great deal of independence, this fact makes working there somewhat unappealing.

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Oumuamua might be artificial lightsail

3:45 pm

A new analysis of the velocity and path of the interstellar object Oumuamua suggests it might be an artificial lightsail.

The study, which was posted online earlier this month, suggests that Oumuamua’s strange “excess acceleration” could be artificial in nature, as it has been implied that it is not an active comet. “Considering an artificial origin, one possibility is that ‘Oumuamua is a lightsail, floating in interstellar space as a debris from an advanced technological equipment,” researchers wrote in the paper.

The paper continues: “Lightsails with similar dimensions have been designed and constructed by our own civilization, including the IKAROS project and the Starshot Initiative. The lightsail technology might be abundantly used for transportation of cargos between planets or between stars.”

They even theorized that Oumuamua “may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization,” though that scenario was called “exotic.”

All of this is speculation. However, that the object is moving faster than expected, based on the initial data of its path, is quite intriguing. The authors of the paper concluded that the excess speed was caused by “solar radiation pressure.” They also calculated that for the light pressure to cause that increase in speed as it moves away requires it to have a large surface area.

The observations are not sufficiently sensitive to provide a resolved image of ‘Oumuamua, and one can only speculate on its possible geometry and nature. Although periodic variations in the apparent magnitude are observed, there are still too many degrees of freedom (e.g., observing angle, non-uniform reflectively, etc.) to definitely constrain the geometry. The geometry should not necessarily be that of a planar sheet, but may acquire other shapes, e.g., involving a curved sheet, a hollow cone or ellipsoidal, etc. Depending on the geometry our estimated value for the mass-to-area ratio will change, but the correction is typically of order unity.

They then speculate the possibility of the object being an interstellar probe.

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Sunspot update October 2018: Deepening minimum

9:04 am

The monthly NOAA update of the solar cycle, covering sunspot activity for October 2018, was released yesterday. As I have done every month since this website began in July 2011, I am posting it below, annotated to give it some context.

Though there was a tiny uptick in sunspot activity on the Sun in October, the uptick was inconsequential. Overall, the activity in the past few months appears to closely match the weak activity seen in late 2007 and early 2008, just when the last solar minimum began.

October 2018 sunspot activity

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.

As I noted in August, the NOAA graph is now getting very close to its right edge, which ends in December 2018. They will very soon have to update this graph so that it can take us into the next solar cycle. While they must do this, it will unfortunately end the standard visual used by them for more than a decade for showing the progress of the solar cycle. Depending on how they change it, I might be able adapt it to include this graph to allow a continuation of the same visual into the future. We will have to see.

Having seen now the full solar maximum for this cycle (weak and short), we are now moving to the next question: Will the developing solar minimum be as long and as deep as the last? Will it evolve into a grand minimum, lasting decades, as some solar scientists believe?

Or will the Sun return to the higher levels of activity seen during most of the 24 solar cycles observed since the last grand minimum in the 1600s?

Since our understanding of these changes is very poor, your guess is likely as good as anyone else’s. All we can really do is keep our eyes open and watch what happens.

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Danish astronomers question gravitational wave detection

9:23 am

The uncertainty of science: A team of Danish astronomers have questioned the gravitational wave detection achieved in the past few years by the LIGO gravitational wave telescopes.

The details are complex and very much in dispute, and the position of these Danish astronomers is very much in the minority, but their doubts have not been dismissed, and illustrate well the best aspects science. The article also outlines how the physics community and the LIGO scientists have welcomed the skepticism, even as they have doubts about the claims of the Danish astronomers. This is the hallmark of good science, and lends weight to the work at LIGO.

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Dawn’s last look at Ceres

10:14 am

Ceres

The Dawn mission has ended, and the image on the right, reduced to post here, is one of its last views of Ceres, with the bright spots of Occator Crater clearly visible, before its fuel ran out. You can see the full resolution image by clicking on the image.

This photo of Ceres and the bright regions in Occator Crater was one of the last views NASA’s Dawn spacecraft transmitted before it depleted its remaining hydrazine and completed its mission.

This view, which faces south, was captured on Sept. 1, 2018 at an altitude of 2,340 miles (3,370 kilometers) as the spacecraft was ascending in its elliptical orbit. At its lowest point, the orbit dipped down to only about 22 miles (35 kilometers), which allowed Dawn to acquire very high-resolution images in this final phase of its mission. Some of the close-up images of Occator Crater are shown here.

Occator Crater is 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep and holds the brightest area on Ceres, Cerealia Facula in its center and Vinalia Faculae in its western side. This region has been the subject of intense interest since Dawn’s approach to the dwarf planet in early 2015.

If NASA made any specific announcement about the end of the mission, I have missed it. Either way, this end is not a surprise, because they have made it clear for the past few months that the spacecraft was about to run out of fuel.

They have also posted today an image of Ceres’ largest mountain, Ahuna Mons.

Update: Even as I posted this, NASA sent out this press release: NASA’s Dawn mission comes to an end

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OSIRIS-REx snaps image of target asteroid Bennu

9:41 am

Bennu

OSIRIS-REx has snapped its sharpest image yet of its target asteroid Bennu, set for a rendezvous on December 3. The image on the right is that image, at full resolution but cropped.

This “super-resolution” view of asteroid Bennu was created using eight images obtained by NASA’s OSIRIS-REx spacecraft on Oct. 29, 2018 from a distance of about 205 miles (330 km). The spacecraft was moving as it captured the images with the PolyCam camera, and Bennu rotated 1.2 degrees during the nearly one minute that elapsed between the first and the last snapshot. The team used a super-resolution algorithm to combine the eight images and produce a higher resolution view of the asteroid. Bennu occupies about 100 pixels and is oriented with its north pole at the top of the image.

It is beginning to appear that the OSIRIS-REx engineering team is going to have the same kind of problems now faced by the Hayabusa-2 engineering team. In this first glance Bennu appears very similar to Ryugu, a rubble pile shaped approximately like a box, rotating on one point. If so, they are also going to find it difficult to locate a smooth landing site.

Bennu by the way is in an orbit that makes a collision with the Earth possible in the late 22nd century. Knowing its composition, density, and solidity is critical for determining what to do, should that collision become likely.

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Parker begins first perihelion fly-by of Sun

9:10 am

It’s getting hot in here: The Parker Solar Probe has begun its first close orbital fly-by of the Sun, set to last from now until November 11.

This solar encounter encompasses the first perihelion of the mission, the point at which Parker Solar Probe is closest to the Sun. Perihelion is expected at about 10:28 p.m. EST on Nov. 5. The spacecraft will come within 15 million miles of the Sun’s surface and clock in at a top speed of 213,200 miles per hour relative to the Sun — setting new records for both closest solar approach and top heliocentric speed by a spacecraft. At perihelion, Parker Solar Probe will fly through material at about 3.6 million degrees Fahrenheit — but because material in this region is so tenuous, it doesn’t influence the temperature of the spacecraft. However, the Sun’s intense radiation heats the Sun-facing side of the spacecraft’s heat shield, called the Thermal Protection System, to about 820 F.

For several days around the Nov. 5 perihelion, Parker Solar Probe will be completely out of contact with Earth because of interference from the Sun’s overwhelming radio emissions.

The article provides some nice details about the spacecraft’s design.

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The vast northern plains of Mars

3:33 pm

The vast northern plains of Mars

Cool image time! Actually, this image, found in the October image release from the high resolution camera of Mars Reconnaissance Orbiter (MRO), is not that interesting, in its own right. Context is all!

The image on the right is a small section cropped and reduced in resolution from the full image, which you can see by clicking on it. It shows one of the only interesting features in this long image strip, a small mesa sticking out all by itself in a flat featureless plain pockmarked by various small craters.

The release has no caption, though it is entitled “Northern Plains Survey.” The northern plains, while having a lot of interesting features that attract the attention of planetary scientists and thus get photographed at high resolution, is mostly featureless, at least at the resolution of the wide field survey cameras on many Mars orbiters. In order to know what is really there, they need to take high resolution images systematically, of which this image is obviously a part.

Overview image

The problem is that there is so much ground to cover. This particular image was taken of a spot in the middle of the plains just to the north of the drainage outlets from Valles Marineris, as shown by the context map to the right. The tiny white spot to the right in the middle of the blue plains north of those drainage outlets is the location of this image.

Detail area of overview map

To understand how much ground needs to be covered, to the right is a close-up of the area shown by the white box in the first image above, with red rectangles indicating where MRO has already taken images. The white cross is the subject image. As you can see, most of this immense plain has not yet been imaged. It is almost as if they threw a dart to pick this one location. Most everything around it remains unseen at high resolution. Thus, to understand the geology of this one image is hampered because the surrounding terrain remains unknown, in close detail.

Mars is a big place. It is an entire planet, with the same land surface as the Earth’s continents. It still contains many mysteries and unexplored places. It will take generations to see it all.

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