Posted on by Matt Williams

Curiosity’s Martian Chronicles Rife With Intriguing Inconsistencies

Bedrock at this site added to a puzzle about ancient Mars by indicating that a lake was present, but that little carbon dioxide was in the air to help keep a lake unfrozen. Credit: NASA/JPL-Caltech/MSSS

The study of Mars’ surface and atmosphere has unlocked some ancient secrets. Thanks to the efforts of the Curiosity rover and other missions, scientists are now aware of the fact that water once flowed on Mars and that the planet had a denser atmosphere. They have also been able to deduce what mechanics led to this atmosphere being depleted, which turned it into the cold, desiccated environment we see there today.

At the same time though, it has led to a rather intriguing paradox. Essentially, Mars is believed to have had warm, flowing water on its surface at a time when the Sun was one-third as warm as it is today. This would require that the Martian atmosphere had ample carbon dioxide in order to keep its surface warm enough. But based on the Curiosity rover’s latest findings, this doesn’t appear to be the case.

These findings were part of an analysis of data taken by the Curiosity’s Chemistry and Mineralogy X-ray Diffraction (CheMin) instrument, which has been used to study the mineral content of drill samples in the Gale Crater. The results of this analysis were recently published in Proceedings of the National Academy of Science, where the research team indicated that no traces of carbonates were found in any samples taken from the ancient lake bed.

Simulated view of Gale Crater Lake on Mars, depicting a lake of water partially filling Mars’ Gale Crater. Credit: NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS

To break it down, evidence collected by Curiosity (and a slew of other rovers, landers and orbiters) has led scientists to conclude that roughly 3.5 billion years ago, Mars surface had lakes and flowing rivers. They have also determined, thanks to the many samples taken by Curiosity since it landed in the Gale Crater in 2011, that this geological feature was once a lake bed that gradually became filled with sedimentary deposits.

However, for Mars to have been warm enough for liquid water to exist, its atmosphere would have had to contain a certain amount of carbon dioxide – providing a sufficient Greenhouse Effect to compensate for the Sun’s diminished warmth. Since rock samples in the Gale Crater act as a geological record for what conditions were like billions of years ago, they would surely contain plenty of carbonate minerals if this were the case.

Carbonates are minerals that result from carbon dioxide combining with positively charged ions (like magnesium and iron) in water. Since these ions have been found to be in good supply in samples of Martian rock, and subsequent analysis has shown that conditions never became acidic to the point that the carbonates would have dissolved, there is no apparent reason why they wouldn’t be showing up.

Along with his team, Thomas Bristow – the principal investigator for the CheMin instrument on Curiosity – calculated what the minimum amount of atmospheric carbon dioxide would need to be, and how this would have been indicated by the levels of carbonate found in Martian rocks today. They then sorted through the years worth of the CheMin instrument’s data to see if there were any indications of these minerals.

Comparison of X-ray diffraction patterns of two different samples analyzed by Curiosity’s Chemistry and Mineralogy (CheMin) instrument. Credit: NASA/JPL-Caltech/Ames

But as he explained in a recent NASA press release, the findings simply didn’t measure up:

“We’ve been particularly struck with the absence of carbonate minerals in sedimentary rock the rover has examined. It would be really hard to get liquid water even if there were a hundred times more carbon dioxide in the atmosphere than what the mineral evidence in the rock tells us.”

In the end, Bristow and his team could not find even trace amounts of carbonates in the rock samples they analyzed. Even if just a few tens of millibars of carbon dioxide had been present in the atmosphere when a lake existed in the Gale Crater, it would have produced enough carbonates for Curiosity’s CheMin to detect. This latest find adds to a paradox that has been plaguing Mars researchers for years.

Basically, researchers have noted that there is a serious discrepancy between what surface features indicate about Mars’ past, and what chemical and geological evidence has to say. Not only is there plenty of evidence that the planet had a denser atmosphere in the past, more than four decades of orbital imaging (and years worth of surface data) have yielded ample geomorphological evidence that Mars once had surface water and an active hydrological cycle.

The Gale Crater – the landing location and trek of the Rover Curiosity – as it is today, imaged by the MRO. Credits: NASA/JPL, illustration, T.Reyes

However, scientists are still struggling to produce models that show how the Martian climate could have maintained the types of conditions necessary for this to have been the case. The only successful model so far has been one in which the atmosphere contained a significant amount of CO2 and hydrogen. Unfortunately, an explanation for how this atmosphere could be created and sustained remains elusive.

In addition, the geological and chemical evidence for such a atmosphere existing billions of years ago has also been in short supply. In the past, surveys by orbiters were unable to find evidence of carbonate minerals on the surface of Mars. It was hoped that surface missions, like Curiosity, would be able to resolve this by taking soil and drill samples where water had been known to exist.

But as Bristow explained, his team’s study has effectively closed the door on this:

“It’s been a mystery why there hasn’t been much carbonate seen from orbit. You could get out of the quandary by saying the carbonates may still be there, but we just can’t see them from orbit because they’re covered by dust, or buried, or we’re not looking in the right place. The Curiosity results bring the paradox to a focus. This is the first time we’ve checked for carbonates on the ground in a rock we know formed from sediments deposited under water.”

Annontated version of the bedrock site in the Gale Crater where the Curiosity rover has taken drill samples. Credit: NASA/JPL-Caltech/MSSS

There are several possible explanations for this paradox. On the one hand, some scientists have argued that the Gale Crater Lake may not have been an open body of water and was perhaps covered in ice, which was just thin enough to still allow for sediments to get in. The problem with this explanation is that if this were true, there would be discernible indications left behind – which would include deep cracks in the soft sedimentary lakebed rock.

But since these indications have not been found, scientists are left with two lines of evidence that do not match up. As Ashwin Vasavada, Curiosity’s Project Scientist, put it:

“Curiosity’s traverse through streambeds, deltas, and hundreds of vertical feet of mud deposited in ancient lakes calls out for a vigorous hydrological system supplying the water and sediment to create the rocks we’re finding. Carbon dioxide, mixed with other gases like hydrogen, has been the leading candidate for the warming influence needed for such a system. This surprising result would seem to take it out of the running.”

Luckily, incongruities in science are what allow for new and better theories to be developed. And as the exploration of the Martian surface continues  – which will benefit from the arrival of the ExoMars and the Mars 2020 missions in the coming years – we can expect additional evidence to emerge. Hopefully, it will help point the way towards a resolution for this paradox, and not complicate our theories even more!

Further Reading: NASA

Posted on by Evan Gough

Cassini Images Of Enceladus Highlight Possible Cradle For Life

Saturn's moon Enceladus, in all its glory. Captured by the Cassini probe. Image: NASA/JPL-Caltech/Space Science Institute

During its long mission to Saturn, the Cassini spacecraft has given us image after spectacular image of Saturn, its rings, and Saturn’s moons. The images of Saturn’s moon Enceladus are of particular interest when it comes to the search for life.

At first glance, Enceladus appears similar to other icy moons in our Solar System. But Cassini has shown us that Enceladus could be a cradle for extra-terrestrial life.

Our search for life in the Solar System is centred on the presence of liquid water. Maybe we don’t know for sure if liquid H2O is required for life. But the Solar System is huge, and the effort required to explore it is immense. So starting our search for life with the search for liquid water is wise. And in the search for liquid water, Enceladus is a tantalizing target.

Cassini captured this image of Enceladus with Saturn’s rings. The vapor plumes are slightly visible at the south polar region (bottom of image). Image: NASA/JPL/Space Science Institute

Though Enceladus looks every bit like a frozen, lifeless world on its surface, it’s what lies beneath its frigid crust that is exciting. Enceladus appears to have a subsurface ocean, at least in it’s south polar region. And that ocean may be up to 10 km. deep.

Before we dive into that, (sorry), here are a few basic facts about Enceladus:

  • Enceladus is Saturn’s sixth largest moon
  • Enceladus is about 500 km in diameter (Earth’s Moon is 3,474 km in diameter)
  • Enceladus was discovered in 1789 by William Herschel
  • Enceladus is one of the most reflective objects in our Solar System, due to its icy surface

In 2005, Cassini first spied plumes of frozen water vapor erupting from the southern polar region. Called cryovolcanoes, subsequent study of them determined that they are the likely source of Saturn’s E Ring. The existence of these plumes led scientists to suspect that their source was a sub-surface ocean under Enceladus’ ice crust.

This close up image of Enceladus clearly shows multiple plumes erupting into space. Image: NASA/JPL/Space Science Institute

Finding plumes of water erupting from a moon is one thing, but it’s not just water. It’s salt water. Further study showed that the plumes also contained simple organic compounds. This advanced the idea that Enceladus could harbor life.

This image of Enceladus shows the features known as “Tiger stripes”. They are the source of the vapor plumes that erupt from the surface. Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

The geysers aren’t the only evidence for a sub-surface ocean on Enceladus. The southern polar region has a smooth surface, unlike the rest of the moon which is marked with craters. Something must have smoothed that surface, since it is next to impossible that the south polar region would be free from impact craters.

In 2005, Cassini detected a warm region in the south, much warmer than could be caused by solar radiation. The only conclusion is that Enceladus has a source of internal heating. That internal heat would create enough geologic activity to erase impact craters.

So now, two conditions for the existence of life have been met: liquid water, and heat.

In 2005, data from Cassini showed that the so-called “Tiger Stripe” features on Enceladus’ south pole region are warm spots. Image:NASA/JPL/GSFC/SwRI/SSI

The source of the heat on Enceladus was the next question facing scientists. That question is far from settled, and there could be several sources of heat operating together. Among all the possible sources for the heat, two are most intriguing when it comes to the search for life: tidal heating, and radioactive heating.

Tidal heating is a result of rotational and orbital forces. In Enceladus’ case, these forces cause friction which is dissipated as heat. This heat keeps the sub-surface ocean in liquid form, but doesn’t prevent the surface from freezing solid.

Radioactive heating is caused by the decay of radioactive isotopes. If Enceladus started out as a rocky body, and if it contained enough short-lived isotopes, then an enormous amount of heat would be produced for several million years. That action would create a rocky core surrounded by ice.

Then, if enough long-lived radioactive isotopes were present, they would continue producing heat for a much longer period of time. However, radioactive heating isn’t enough on its own. There would have to be tidal heating also.

Gravity measurements by NASA’s Cassini spacecraft and Deep Space Network suggest that Saturn’s moon Enceladus, which has jets of water vapor and ice gushing from its south pole, also harbors a large interior ocean beneath an ice shell, as this illustration depicts.
Image Credit:
NASA/JPL-Caltech

More evidence for a large, sub-surface ocean came in 2014. Cassini and the Deep Space Network provided gravitometric measurements showing that the ocean is there. Those measurements showed that there is likely a regional, if not global, ocean some 10 km thick. Measurements also showed that the ocean is under an ice layer 30 to 40 km thick.

This close up image of Enceladus show the variability of its icy features. The dark spots were originally called “Dalmatian” terrain when first imaged in 2005. There exact nature remained a mystery until ten years later, when Cassini flybys showed that they are actually blocks of bedrock ice scattered along a ridge. The blocks range in size from tens to hundreds of meters. Image: NASA/JPL/Cal-Tech.

The discovery of a warm, salty ocean containing organic molecules is very intriguing, and has expanded our idea of what the habitable zone might be in our Solar System, and in others. Enceladus is much too distant from the Sun to rely on solar energy to sustain life. If moons can provide their own heat through tidal heating or radioactive heating, then the habitable zone in any solar system wouldn’t be determined by proximity to the star or stars at the centre.

Cassini’s mission is nearing its end, and it won’t fly by Enceladus again. It’s told us all it can about Enceladus. It’s up to future missions to expand our understanding of Enceladus.

Numerous missions have been talked about, including two that suggest flying through the plumes and sampling them. One proposal has a sample of the plumes being returned to Earth for study. Landing on Enceladus and somehow drilling through the ice remains a far-off idea better left to science fiction, at least for now.

Whether or not Enceladus can or does harbor life is a question that won’t be answered for a long time. In fact, not all scientists agree that there is a liquid ocean there at all. But whether it does or doesn’t harbor life, Cassini has allowed us to enjoy the tantalizing beauty of that distant object.

Enceladus. Cassini Imaging Team, SSI, JPL, ESA, NASA
Posted on by Nancy Atkinson

A Black Hole’s Record Breaking Lunch

A trio of X-ray observatories has captured a decade-long eating binge by a black hole almost two billion light years away. Credit: X-ray: NASA/CXC/UNH/D.Lin et al, Optical: CFHT, Illustration: NASA/CXC/M.Weiss.

Does a distant black hole provide a new definition of pain and suffering?

The black hole, named XJ1500+0154, appears to be the real-life equivalent of the Pit of Carkoon, the nesting place of the all-powerful Sarlacc in Star Wars, which slowly digested its victims.

Over ten years ago, this giant black hole ripped apart a star and has since continued a very long lunch, feasting on the stars’ remains. Astronomers have been carefully monitoring this slow ‘digestion,’ because it is so unusual for what are called tidal disruption events (TDEs), where tidal forces from black holes tear stars apart.

“We have witnessed a star’s spectacular and prolonged demise,” said Dacheng Lin from the University of New Hampshire in Durham, New Hampshire, who led the observations of this event. “Dozens of tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one.”

This artist’s illustration depicts what astronomers call a “tidal disruption event,” or TDE, when an object such as a star wanders too close to a black hole and is destroyed by tidal forces generated from the black hole’s intense gravitational forces. (Credit: NASA/CXC/M.Weiss.

This decade-long feast has gone on ten times longer than any other observed TDE.

XJ1500+0154 is located in a small galaxy about 1.8 billion light years from Earth, and three telescopes have been monitoring this X-ray event: the Chandra X-ray Observatory, the Swift satellite, and the XMM-Newton.

TDEs are different from another, more common black-hole related source of X-rays in the galaxy, active galactic nuclei (AGN). Like the digestion of the Sarlacc, AGNs really can last for thousands of years. These are supermassive black holes at the center of galaxies that pull in surrounding gas and “emit copious amounts of radiation, including X-rays,” explained Lin in a blog post on the Chandra website. “Radiation from AGNs do not vary a lot because the gas surrounding them extends over a large scale and can last for tens of thousands of years.”

In contrast, TDEs are relatively short-lived, lasting only a few months. During a TDE, some of the stellar debris is flung outward at high speeds, while the rest falls toward the black hole. As it travels inwards to be consumed by the black hole, the material heats up to millions of degrees, generating a distinct X-ray flare.

XJ1500+0154 has provided an extraordinarily long, bright phase, spanning over ten years. Lin and his team said one explanation could be the most massive star ever to be completely torn apart during a TDE.

“To have the event last so long at such high luminosity requires full disruption of a relatively massive star, about twice the mass of the sun,” Lin wrote; however, “disruption of such massive stars by the SMBH is very unlikely because stars this massive are rare in most galaxies, unless the galaxy is young and actively forming stars, as in our case.

So, another more likely explanation is that this is the first TDE observed where a smaller star was completely torn apart.

Lin also said this event has broad implications for black hole physics.

An X-ray image of the full field of view by of the region where the ‘tidal disruption event’ is taking place. The purple smudge in the lower right shows the disruption from the black hole XJ1500+0154. Credit: X-ray: NASA/CXC/UNH/D.Lin et al.

“To fully explain the super-long duration of our event requires the application of recent theoretical progress on the study of TDEs,” he wrote. “In the last two years, several groups independently found that it can take a long time after the disruption of the star for the stellar debris to settle onto the accretion disk and into the SMBH. Therefore, the event can evolve much more slowly than previously thought.”

Additionally, the X-ray data also indicate that radiation from material surrounding this black hole has consistently surpassed what is called the Eddington limit, which is defined as a balance between the outward pressure of radiation from the hot gas and the inward pull of the gravity of the black hole.

Seeing evidence of such rapid growth may help astronomers understand how supermassive black holes were able to reach masses about a billion times higher than the sun when the universe was only about a billion years old.

“This event shows that black holes really can grow at extraordinarily high rates,” said co-author Stefanie Komossa of QianNan Normal University for Nationalities in Duyun City, China. “This may help understand how precocious black holes came to be.”

Lin and his team will continue to monitor this event, and they expect the X-ray brightness to fade over the next few years, meaning the supply of ‘food’ for this long lunch will soon be consumed.

For further reading:
Paper: A likely decade-long sustained tidal disruption event
Lin’s blog post on the Chandra website
Chandra press release
Additional images and information from Chandra

Posted on by Bob King

See a Flirtatious Lunar Eclipse This Friday Night

Penumbral lunar eclipse Oct. 18-19, 2013. Credit: AstroTripper2000
This sequence of photos taken on October 18, 2013 nicely show the different phases of a penumbral lunar eclipse. The coming penumbral eclipse will likely appear even darker because Earth’s shadow will shade to the top (northern) half of the Moon rich in dark lunar “seas” at maximum. Credit: AstroTripper 2000

Not many people get excited about a penumbral eclipse, but when it’s a deep one and the only lunar eclipse visible in North America this year, it’s worth a closer look. What’s more, this Friday’s eclipse happens during convenient, early-evening viewing hours. No getting up in the raw hours before dawn.

Lunar eclipses — penumbral, partial and total — always occur at Full Moon, when the Moon, Earth and Sun line up squarely in a row in that order. Only then does the Moon pass through the shadow cast by our planet. Credit: Starry Night with additions by the author

During a partial or total lunar eclipse, the full moon passes first through the Earth’s outer shadow, called the penumbra, before entering the dark, interior shadow or umbra. The penumbra is nowhere near as dark as the inner shadow because varying amounts of direct sunlight filter into it, diluting its duskiness.

To better understand this, picture yourself watching the eclipse from the center of the Moon’s disk (latitude 0°, longitude 0°). As you look past the Earth toward the Sun, you would see the Sun gradually covered or eclipsed by the Earth. Less sunlight would be available to illuminate the Moon, so your friends back on Earth would notice a gradual dimming of the Moon, very subtle at first but becoming more noticeable as the eclipse progressed.

This diagram shows an approximation of the Sun’s position and size as viewed by an observer at the center of the lunar disk during Friday’s penumbral eclipse. More sunlight shines across the Moon early in the eclipse, making the penumbral shadow very pale, but by maximum (right), half the sun is covered and the Moon appears darker and duskier as seen from Earth. During a total lunar eclipse, the sun is hidden completely. Credit: Bob King with Earth image by NASA

As the Moon’s leading edge approached the penumbra-umbra border, the Sun would narrow to a glaring sliver along Earth’s limb for our lucky lunar observer. Back on Earth, we’d notice that the part of the Moon closest to the umbra looked strangely gray and dusky, but the entire lunar disk would still be plainly visible. That’s what we’ll see during Friday’s eclipse. The Moon will slide right up to the umbra and then roll by, never dipping its toes in its dark waters.

During a partial eclipse, the Moon keeps going into the umbra, where the Sun is completely blocked from view save for dash of red light refracted by the Earth’s atmosphere into what would otherwise be an inky black shadow. This eclipse, the Moon only flirts with the umbra.

The moon’s orbit is tilted 5.1 degrees in relation to Earth’s orbit, so most Full Moons, it passes above or below the shadow and no eclipse occurs. Credit: Bob King

Because the moon’s orbit is tilted about 5° from the plane of Earth’s orbit, it rarely lines up for a perfect bullseye total eclipse: Sun – Earth – Moon in a straight line in that order. Instead, the moon typically passes a little above or below (north or south) of the small, circle-shaped shadow cast by our planet, and no eclipse occurs. Or it clips the outer edge of the shadow and we see — you guessed it — a penumbral eclipse.

Earth’s shadow varies in size depending where you are in it. Standing on the ground during twilight, it can grow to cover the entire sky, but at the moon’s distance of 239,000 miles, the combined penumbra and umbra span just 2.5° of sky or about the width of your thumb held at arm’s length.

The moon passes through Earth’s outer shadow, the penumbra, on Feb. 10-11. In the umbra, the sun is blocked from view, but the outer shadow isn’t as dark because varying amounts of sunlight filter in to dilute the darkness. Times are Central Standard. Credit: F. Espenak, NASA’s GFSC with additions by the author

Because the Moon travels right up to the umbra during Friday’s eclipse, it will be well worth watching.The lower left  or eastern half of the moon will appear obviously gray and blunted especially around maximum eclipse as it rises in the eastern sky that Friday evening over North and South America. I should mention here that the event is also visible from Europe, Africa, S. America and much of Asia.

This map shows where the eclipse will be visible. Most of the U.S. will see at least part of the event. Credit: F. Espenak, NASA’s GFSC

For the U.S., the eastern half of the country gets the best views. Here are CST and UT times for the different stages. To convert from CST, add an hour for Eastern, subtract one hour for Mountain and two hours for Pacific times. UT stands for Universal Time, which is essentially the same as Greenwich or “London” Time except when Daylight Saving Time is in effect:

This is a simulated view of the Full Snow Moon at maximum eclipse Friday evening low in the eastern sky alongside the familiar asterism known as the Sickle of Leo. Created with Stellarium

Eclipse begins: 4:34 p.m. (22:34 p.m. UT)
Maximum eclipse (moon deepest in shadow): 6:44 p.m. (00:43 UT Feb. 11)
Eclipse ends: 8:53 p.m. (2:53 UT Feb. 11)

You can see that the eclipse plays out over more than 4 hours, though I don’t expect most of us will either be able or would want to devote that much time. Instead, give it an hour or so when the Moon is maximally in shadow from 6 to 7:30 p.m. CST; 7-8:30 EST; 5-6:30 p.m. MST and around moonrise Pacific time.

This should be a fine and obvious eclipse because around the time of maximum, the darkest part of the penumbra shades the dark, mare-rich northern hemisphere of the Moon. Dark plus dark equals extra dark! Good luck and clear skies!

Posted on by Matt Williams

The Race To Image Exoplanets Heats Up!

Comparison of images taken from existing, facility instrument (AO 188 + HiCIAO, left) and the newly commissioned instrument (AO 188 + SCExAO, right). Credit: NAOJ

Thanks to the deployment of the Kepler mission, thousands of extrasolar planet candidates have been discovered. Using a variety of indirect detection methods, astronomers have detected countless gas giants, super Earths, and other assorted bodies orbiting distant stars. And one terrestrial planet (Proxima b) has even been found lurking in the closest star system to Earth – Proxima Centauri.

The next step, quite logically, is to observe these planets directly. Hence why the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument was commissioned at the National Astronomical Observatory of Japan (NAOJ) in  Mauna Kea, Hawaii. Designed to allow for the direct detection of planets around other stars, this instrument will help ensure that the Subaru Telescope remains on the cutting-edge of exoplanet hunting.

As of January 22nd, 2017, some 3,565 exoplanet candidates have been detected in 2,675 planetary systems, and over 2000 of these have been confirmed. However, as already noted, the vast majority of these have been detected by  indirect means – generally through the measurement of a star’s radial velocity, or by measuring dips in a star’s luminosity as an exoplanet passes in front of it (i.e. the transit method).

The Subaru Telescope atop Mauna Kea. CHARIS works in conjunction with Subaru. Image: Dr. Hideaki Fujiwara - Subaru Telescope, NAOJ.
The Subaru Telescope atop Mauna Kea. CHARIS works in conjunction with Subaru. Credit: Dr. Hideaki Fujiwara/NAOJ

Adaptive Optics, meanwhile, have allowed for the detection of exoplanets directly. When used in astronomy, this technology removes the the effects of atmospheric interference so that light from distant stars or planets can be seen clearly. Relying on experimental technology, the SCExAO was specifically designed and optimized for imaging planets, and is one of several newly-commissioned extreme AO instruments.

However, as Dr. Thayne Currie – a research associate at the NOAJ – indicated, the Observatories on Mauna Kea are particularly well suited to the technology. “Mauna Kea is the best place on this planet to see planets in other stellar systems,” he said. “Now, we finally have an instrument designed to utilize this mountain’s special gifts and the results are breathtaking.”

What makes the SCExAO special is that it allows astronomers the ability to image planets with masses and orbital separations that are similar to those in our own Solar System. So far, about a dozen planets have been detected directly using AO instruments, but these planets have all been gas giants with 4 to 13 times the mass of Jupiter, and which orbit their stars at distances beyond that of Neptune from our Sun.

This improved imaging capacity is made possible by the SCExAO’s ability to compensate for atmospheric interference at a faster rate. This will enable the Subaru Telescope to be able to capture far images of distant stars that are sharper and subject to less glare. And astronomers will be able to discern the presence of fainter objects that are circling these stars – i.e. exoplanets – with greater ease.

The debris disk detected around a young star HD 36546 using SCExAO/HiCIAO (left, seen nearly edge-on) and its model (right, viewed face-on). Credit: NAOJ

The first discovery made with the SCExAO, took place back in October of 2016. At the time, the Subaru telescope had detected a debris disk around HD 36546 – a 2 solar-mass star in the direction of the Taurus constellation – which appeared almost edge on. Located about twice as far from HD 36546 as the Kuiper Belt is from our Sun, this disk is believed to be the youngest debris disk ever observed (3 to 10 million years old).

This test of the SCExAO not only revealed a disk that could be critical to studying the earliest stages of icy planet formation, but demonstrated the extreme sensitivity of the technology. Basically, it allowed the astronomers conducting the study to rule out the existence of any planets in the system, thus concluding that planetary dynamics played no role in sculpting the disk.

More recently, the SCExAO instrument managed to directly detect multiple planets in the system known as HR 8799, which it observed in July of 2016. Prior to this, some of the systems four planets were spotted by surveys conducted using the Keck and the Subaru telescope (before the SCExAO was incorporated). However, these surveys could not correct for all the glare coming from HR 8799, and could only image two of three of the planets as a result.

A follow-up was conducted in the Fall of 2016, combining data from the SCExAO with that obtained by the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS). This resulted in even clearer detection of the system’s inner three planets, not to mention high-quality spectrographic data that could allow researchers to determine the chemical compositions of their atmospheres.

The star and multiple planet system HR 8799 imaged using the SCEAO and the HiCIAO camera (left) and the Keck facility AO system coupled with the NIRC2 camera (right). Credit: NAOJ

As Dr. Olivier Guyon, the head of the SCExAO project, explained, this is a major improvement over other AO surveys. It also presents some major advantages when it comes to exoplanet hunting. “With SCExAO, we know not only the presence of a planet but also its character such as whether it is cloudy and what molecules it has, even if that planet is tens of trillions of miles away.”

Looking at the year ahead, the SCExAO is scheduled to undergo improvements that will allow it to detect planets that are 10 to 10o times fainter than what it can right now. The CHARIS instrument is also scheduled for additional engineering tests to improve its capabilities. These improvements are also expected to be incorporated into next-generation telescopes like the Thirty Meter Telescope – which is currently under construction at Mauna Kea.

Other recently-commissioned extreme AO instruments include the Gemini Planet Imager (GPI) at Gemini Observatory on its telescope in Chile, the Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) on Very Large Telescope (VLT) in Chile, and the AO system on the Large Binocular Telescope (LBT) in Arizona. And these are only some of the current attempts to reduce interference and make exoplanets easier to detect.

For instance, coronagraph are another way astronomers are attempting to refine their search efforts. Consisting of tiny instruments that are fitted inside telescopes, coronagraphs block the incoming light of a star, thus enabling telescopes to spot the faint light being reflected from orbiting planets. When paired with spectrometers, scientists are able to conduct studies of these planet’s atmospheres.

An artist's illustration of the Starshade deployed near its companion telescope. Image: NASA
An artist’s illustration of the Starshade deployed near its companion space telescope. Credit: NASA

And then you have more ambitious projects like Starshade, a concept currently being developed by Northrop Grumman with the support of NASA’s Jet Propulsion Laboratory. This concept calls for a giant, flower-shaped screen that would be launched with one of NASA’s next-generation space telescopes. Once deployed, it would fly around in front of the telescope in order to obscure the light coming from distant stars.

The era of exoplanet discovery loometh! In the coming decades, we are likely to see an explosion in the number of planets were are able to observe directly. And in so doing, we can expect the number of potentially habitable exoplanets to grow accordingly.

Further Reading: NAOJ/Subaru Telescope

Posted on by Evan Gough

Meteorite Confirms 2 Billion Years of Volcanic Activity on Mars

Color Mosaic of Olympus Mons on Mars
Olympus Mons on Mars is the largest volano in our Solar System. Analysis of a Martian meteorite that fell to Earth in 2012 confirms that Mars also has the longest-lived volcanoes in our Solar System. Image: NASA/JPL

Mars is renowned for having the largest volcano in our Solar System, Olympus Mons. New research shows that Mars also has the most long-lived volcanoes. The study of a Martian meteorite confirms that volcanoes on Mars were active for 2 billion years or longer.

A lot of what we know about the volcanoes on Mars we’ve learned from Martian meteorites that have made it to Earth. The meteorite in this study was found in Algeria in 2012. Dubbed Northwest Africa 7635 (NWA 7635), this meteorite was actually seen travelling through Earth’s atmosphere in July 2011.

A sample from the meteorite Northwest Africa 7635. Image: Mohammed Hmani
A sample from the meteorite Northwest Africa 7635. Image: Mohammed Hmani

The lead author of this study is Tom Lapen, a Geology Professor at the University of Houston. He says that his findings provide new insights into the evolution of the Red Planet and the history of volcanic activity there. NWA 7635 was compared with 11 other Martian meteorites, of a type called shergottites. Analysis of their chemical composition reveals the length of time they spent in space, how long they’ve been on Earth, their age, and their volcanic source. All 12 of them are from the same volcanic source.

Mars has much weaker gravity than Earth, so when something large enough slams into the Martian surface, pieces of rock are ejected into space. Some of these rocks eventually cross Earth’s path and are captured by gravity. Most burn up, but some make it to the surface of our planet. In the case of NWA 7635 and the other meteorites, they were ejected from Mars about 1 million years ago.

“We see that they came from a similar volcanic source,” Lapen said. “Given that they also have the same ejection time, we can conclude that these come from the same location on Mars.”

Taken together, the meteorites give us a snapshot of one location of the Martian surface. The other meteorites range from 327 million to 600 million years old. But NWA 7635 was formed 2.4 billion years ago. This means that its source was one of the longest lived volcanoes in our entire Solar System.

This false color X-ray of NWA 7635 shows the meteorite’s mineralogy mineral textures. O, olivine; P, plagioclase (maskelynite); C, clinopyroxene (augite). Chemical compositions: Fe (purple), Mg (green), Ca (blue), Ti (magenta), and S (yellow). Purple colors in the mesostasis represent Fe-rich augite. You’re welcome, mineral nerds. Image: Lapen et. al.

Volcanic activity on Mars is an important part of understanding the planet, and whether it ever harbored life. It’s possible that so-called super-volcanoes contributed to extinctions here on Earth. The same thing may have happened on Mars. Given the massive size of Olympus Mons, it could very well have been the Martian equivalent of a super-volcano.

The ESA’s Mars Express Orbiter sent back images of Olympus Mons that showed possible lava flows as recently as 2 million years ago. There are also lava flows on Mars that have a very small number of impact craters on them, indicating that they were formed recently. If that is the case, then it’s possible that Martian volcanoes will be visibly active again.

A colorized image of the surface of Mars taken by the Mars Reconnaissance Orbiter. The line of three volcanoes is the Tharsis Montes, with Olympus Mons to the northwest. Valles Marineris is to the east. Image: NASA/JPL-Caltech/ Arizona State University
A colorized image of the surface of Mars taken by the Mars Reconnaissance Orbiter. The line of three volcanoes is the Tharsis Montes, with Olympus Mons to the northwest. Valles Marineris is to the east. Image: NASA/JPL-Caltech/ Arizona State University

Continuing volcanic activity on Mars is highly speculative, with different researchers arguing for and against it. The relatively crater-free, smooth surfaces of some lava features on Mars could be explained by erosion, or even glaciation. In any case, if there is another eruption on Mars, we would have to be extremely lucky for one of our orbiters to see it.

But you never know.

Posted on by Matt Williams

A Novel Concept For Braking Breakthrough Starshot

Artist concept of lightsail craft approaching the potentially habitable exoplanet Proxima b. Credit: PHL @ UPR Arecibo

In April of 2016, Russian billionaire Yuri Milner announced the creation of Breakthrough Starshot. As part of his non-profit scientific organization (known as Breakthrough Initiatives), the purpose of Starshot was to design a lightsail nanocraft that would be capable of reaching the nearest star system – Alpha Centauri (aka. Rigel Kentaurus) – within our lifetime.

Since its inception, the scientists and engineers behind the Starshot concept have sought to address the challenges that such a mission would face. Similarly, there have been many in the scientific community who have also made suggestions as to how such a concept could work. The latest comes from the Max Planck Institute for Solar System Research, where two researchers came up with a novel way of slowing the craft down once it reaches its destination.

To recap, the Starshot concept involves a small, gram-scale nanocraft being towed by a lightsail. Using a ground-based laser array, this lightsail would be accelerated to a velocity of about 60,000 km/s (37,282 mps) – or 20% the speed of light. At this speed, the nanocraft would be able to reach the closest star system to our own – Alpha Centauri, located 4.37 light-years away – in just 20 years time.

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

Naturally, this presents a number of technical challenges – which include the possibility of a collision with interstellar dust, the proper shape of the lightsail, and the sheer energy requirements for powering the laser array. But equally important is the idea of how such a craft would slow down once it reached its destination. With no lasers at the other end to apply breaking energy, how would the craft slow down enough to begin studying the system?

It was this very question that René Heller and Michael Hippke chose to address in their study, “Deceleration of high-velocity interstellar photon sails into bound orbits at Alpha Centauri“. Heller is an astrophysicts who is currently assisting the ESA with its preparations for the upcoming PLAnetary Transits and Oscillations of stars (PLATO) mission – an exoplanet hunter being deployed as part of their Cosmic Vision program.

With the help IT specialist Michael Hippke, the two considered what would be needed for interstellar mission to reach Alpha Centauri, and provide good scientific returns upon its arrival. This would require that braking maneuvers be conducted once it arrived so the the spacecraft would not overshoot the system in the blink of an eye. As they state in their study:

“Although such an interstellar probe could reach Proxima 20 years after launch, without propellant to slow it down it would traverse the system within hours. Here we demonstrate how the stellar photon pressures of the stellar triple Alpha Cen A, B, and C (Proxima) can be used together with gravity assists to decelerate incoming solar sails from Earth.”

The projected path a lightsail mission to Alpha Centauri could take, which would allow it to detour to Proxima Centauri. Credit: PHL @ UPR Arecibo.

For the sake of their calculations, Heller and Hippke estimated that the craft would weigh less than 100 grams (3.5 ounces), and would be mounted on a sail measuring 100,000 m² (1,076,391 square foot) in surface area. Once these were complete, Hippke adapted them into a series of computer simulations. Based on their results, they proposed an entirely new mission concept that do away with the need for lasers entirely.

In essence, their revised concept called for an Autonomous Active Sail (AAS) craft that would provide for its own propulsion and stopping power. This craft would deploy its sail while in the Solar System and use the Sun’s solar wind to accelerate it to high speeds. Once it reached the Alpha Centauri System, it would redeploy its sail so that incoming radiation from Alpha Centauri A and B would have the effect of slowing it down.

An added bonus of this proposed maneuver is that the craft, once it had been decelerated to the point that it could effectively explore the Alpha Centauri system, could then use a gravity assist from these stars to reroute itself towards Proxima Centauri. Once there, it could conduct the first up-close exploration of Proxima b – the closest exoplanet to Earth – and determine what its atmospheric and surface conditions are like.

Since the existence of this planet was first announced by the European Southern Observatory back in August of 2016, there has been much speculation about whether or not it could be habitable. Having a mission that could examine it to check for the telltale markers – a viable atmosphere, a magnetosphere, and liquid water on the surface – would surely settle that debate.

As Heller explained in a press release from the Max Planck Institute, this concept presents quite a few advantages, but comes with its share of trade offs – not the least of which is the time it would take to get to Alpha Centauri. “Our new mission concept could yield a high scientific return, but only the grandchildren of our grandchildren would receive it,” he said. “Starshot, on the other hand, works on a timescale of decades and could be realized in one generation. So we might have identified a longterm, follow-up concept for Starshot.”

At present, Heller and Hippke are discussing their concept with Breakthrough Starshot to see if it would be viable. One individual who has looked over their work is Professor Avi Loeb, the Frank B. Baird Jr. Professor of Science at Harvard University, and the chairman of the Breakthrough Foundation’s Advisory Board. As he told Universe Today via email, the concept put forth by Heller and Hippke is worthy of consideration, but has its limitations:

“If it is possible to slow down a spacecraft by starlight (and gravitational assist), then it is also possible to launch it in the first place by the same forces… If so, why is the recently announced Breakthrough Starshot project using a laser and not Sunlight to propel our spacecraft? The answer is that our envisioned laser array can push the sail with an energy flux that is a million times larger than the local solar flux.

“In using starlight to reach relativistic speeds, one must use an extremely thin sail. In the new paper, Heller and Hippke consider the example of a milligram instead of a gram-scale sail. For a sail of area ten square meters (as envisioned in our Starshot concept study), the thickness of their sail must be only a few atoms. Such a surface is orders of magnitude thinner than the wavelength of light that it aims to reflect, and so its reflectivity would be low. It does not appear feasible to reduce the weight by so many orders of magnitude and yet maintain the rigidity and reflectivity of the sail material.

“The main constraint in defining the Starshot concept was to visit Alpha Centauri within our lifetime. Extending the travel time beyond the lifetime of a human, as advocated in this paper, would make it less appealing to the people involved. Also, one should keep in mind that the sail must be accompanied by electronics which will add significantly to its weight.”

In short, if time is not a factor, we can envision that our first attempts to reach another Solar System may indeed involve an AAS being propelled and slowed down by solar wind. But if we’re willing to wait centuries for such a mission to be completed, we might also consider sending rockets with conventional engines (possibly even crewed ones) to Alpha Centauri.

But if we are intent on getting there within our own lifetimes, then a laser-driven sail or something similar will have be the way to go. Humanity has spent over half a century exploring what’s in our own backyard, and some of us are impatient to see what’s next door!

Further Reading: Max Planck Institute, ArXiv

Posted on by Evan Gough

Preleminary Results In NASA Twins Study Released

NASA's astronauts twins, Scott Kelly (l) and Mark Kelly (r). Image: NASA
NASA's astronaut twins, Scott Kelly (l) and Mark Kelly (r). Image: NASA

In 1996, something remarkable happened at NASA. Twin brothers Mark and Scott Kelly were accepted into NASA; Mark as a shuttle pilot, and Scott into technical operations on the ground, at least initially. Eventually, both brothers became astronauts. They are the only siblings to have both been in space.

Whether it was intentional or not, having twin brothers gave NASA an important opportunity. They could use one twin as a control group, and send the other on a prolonged mission into space. That allowed NASA to carry out important research on the effects of space travel on the human body.

In March 2016, Scott Kelly returned from a year long (340 days) mission aboard the International Space Station, while his brother Mark stayed on Earth. Genetic samples were taken from each brother before and after Scott’s time aboard the ISS. Now, NASA has released the preliminary results of this unprecedented opportunity.

Expedition 46 Commander Scott Kelly of NASA is seen after returning to Ellington Field, Thursday, March 3, 2016 in Houston, Texas after his return to Earth the previous day. Kelly and Flight Engineers Mikhail Kornienko and Sergey Volkov of Roscosmos landed in their Soyuz TMA-18M capsule in Kazakhstan on March 1 (Eastern time).

NASA’s Human Research Program did the study, and the results were released at their Investigator’s Workshop on the week of January 23rd. The theme of that workshop was A New Dawn: Enabling Human Space Exploration. Though the studies are on-going, these initial results are interesting.

Omics

Mike Snyder, who is the Integrated Omics investigator, reported his findings. He found an altered level of lipids in Scott, the flight twin, which indicates inflammation. He also found increased 3-indolepropionic (IPA) in Mark, the ground twin. IPA is a potential brain antioxidant therapeutic, and also helps maintain normal insulin levels, to stabilize blood sugar after meals.

Telomeres and Telomerase

Telomeres and Telomerase are part of the chromosomal system in the human body. Susan Bailey reported that for Scott, the flight twin, the length of his white blood cell’s telomeres increased while in space. Typically, they decrease as a person ages. Once on Earth, they began to shorten again.

Telomerase, an enzyme that repairs telomeres, increased in both brothers in November, which could be related to a stressful family event at that time.

The Soyuz TMA-18M spacecraft is seen as it lands with Expedition 46 Commander Scott Kelly of NASA and Russian cosmonauts Mikhail Kornienko and Sergey Volkov in Kazakhstan on Wednesday, March 2, 2016. Photo Credit: (NASA/Bill Ingalls)

Cognitive Performance in Spaceflight

Mathias Basner is studying Cognitive Performance in Spaceflight, especially the difference in cognition between a 12-month mission and a six-month mission. Though he found a slight decrease in speed and accuracy after the mission, he found no real difference in cognition between 6 month and 12 month missions.

Biochemistry

Scott Smith’s investigation into biochemistry showed a decrease in bone density during the second half of Scott’s mission. Scott also had increased levels of a biochemical marker for inflammation once he returned to Earth.

Microbiome in the Gastro-Intestinal Tract

Fred Turek reported preliminary results of his investigation into the bacteria in the GI (microbiome) tract that help digestion. There were many differences in the twins’ biomes, but that was expected because of their different diets and environments. There were interesting differences in Scott’s biome between his time in space and his time on the ground. The ratio between two dominant bacterial groups shifted during his flight time compared to his ground time.

Immunome Studies

Emmanuel Mignot investigated changes in the bodies of both twins before and after a flu vaccine was given. Both twins showed increased levels of T-cell receptors after the vaccine, which was the expected immune response.

Genome Sequencing

Chris Mason is performing Genome Sequencing on the DNA and RNA contained within the twins’ white blood cells with his investigation. RNA sequencing showed that over 200,000 RNA molecules were expressed differently between the twins. Mason will look closer to see if a “space gene” could have been activated while Scott was in space.

Epigenomics

Andy Feinberg studies how the environment regulates our gene expression, which is known as epigenomics. Scott’s white blood cell DNA showed decreased levels of chemical modification while in flight, and a return to normal once back on Earth. The same level in Mark (the ground twin) increased midway through the study, but then returned to normal. There was variability between the twins, called epigenetic noise. This noise was higher in Scott during his spaceflight, and returned to baseline levels once back on Earth. This could indicate that some genes are more sensitive to the changing environment of spaceflight than others.

There’s a lot more research required to truly understand these results. Once they’re looked at in coordination with other physiological, psychological, and technological investigations, the picture will become clearer. Later in 2017, there will be a joint publication of further results, as well as individual research papers.

NASA’s goal is to make space travel safer for astronauts, and to make missions more effective and efficient. With all the talk of missions to Mars in the next decade, these results are arriving at the perfect time.

Posted on by Evan Gough

Vortex Coronagraph A Game Changer For Seeing Close In Exoplanets

The vortex coronagraph at the Keck Observatory captured this image of the protoplanetary disk surrounding the young star HD 141569. which is about 380 light years from Earth. Image: NASA/JPL-Caltech
The vortex coronagraph at the Keck Observatory captured this image of the protoplanetary disk surrounding the young star HD 141569, which is about 380 light years from Earth. Image: NASA/JPL-Caltech

The study of exoplanets has advanced a great deal in recent years, thanks in large part to the Kepler mission. But that mission has its limitations. It’s difficult for Kepler, and for other technologies, to image regions close to their stars. Now a new instrument called a vortex coronagraph, installed at Hawaii’s Keck Observatory, allows astronomers to look at protoplanetary disks that are in very close proximity to the stars they orbit.

The problem with viewing disks of dust, and even planets, close to their stars is that stars are so much brighter than objects that orbit them. Stars can be billions of times brighter than the planets near them, making it almost impossible to see them in the glare. “The power of the vortex lies in its ability to image planets very close to their star, something that we can’t do for Earth-like planets yet,” said Gene Serabyn of NASA’s Jet Propulsion Laboratory (JPL). “The vortex coronagraph may be key to taking the first images of a pale blue dot like our own.”

“The power of the vortex lies in its ability to image planets very close to their star, something that we can’t do for Earth-like planets yet.” – Gene Serabyn, JPL.

“The vortex coronagraph allows us to peer into the regions around stars where giant planets like Jupiter and Saturn supposedly form,” said Dmitri Mawet, research scientist at NASA’s Jet Propulsion Laboratory and Caltech, both in Pasadena. “Before now, we were only able to image gas giants that are born much farther out. With the vortex, we will be able to see planets orbiting as close to their stars as Jupiter is to our sun, or about two to three times closer than what was possible before.”

Rather than masking the light of stars, like other methods of viewing exoplanets, the vortex coronagraph redirects light away from the detectors by combining light waves and cancelling them out. Because there is no occulting mask, the vortex coronagraph can capture images of regions much closer to stars than other coronagraphs can. Dmitri Mawet, research scientist who invented the new coronagraph, compares it to the eye of a storm.

The vortex mask shown at left is made out of synthetic diamond. When viewed with a scanning electron microscope, right, the "vortex" microstructure of the mask is revealed. Image credit: University of Liège/Uppsala University
The vortex mask shown at left is made out of synthetic diamond. When viewed with a scanning electron microscope, right, the “vortex” microstructure of the mask is revealed. Image credit: University of Liège/Uppsala University

“The instrument is called a vortex coronagraph because the starlight is centered on an optical singularity, which creates a dark hole at the location of the image of the star,” said Mawet. “Hurricanes have a singularity at their centers where the wind speeds drop to zero — the eye of the storm. Our vortex coronagraph is basically the eye of an optical storm where we send the starlight.”

The results from the vortex coronagraph are presented in two papers (here and here) published in the January 2017 Astronomical Journal. One of the studies was led by Gene Serabyn of JPL, who is also head of the Keck vortex project. That study presented the first direct image of HIP79124 B, a brown dwarf that is 23 AU from its star, in the star-forming region called Scorpius-Centaurus.

The vortex coronagraph captured this image of the brown dwarf PIA21417.
The vortex coronagraph captured this image of the brown dwarf PIA21417. Image: NASA/JPL-Caltech

“The ability to see very close to stars also allows us to search for planets around more distant stars, where the planets and stars would appear closer together. Having the ability to survey distant stars for planets is important for catching planets still forming,” said Serabyn.

“Having the ability to survey distant stars for planets is important for catching planets still forming.” – Gene Serabyn, JPL.

The second of the two vortex studies presented images of a protoplanetary disk around the young star HD141569A. That star actually has three disks around it, and the coronagraph was able to capture an image of the innermost ring. Combining the vortex data with data from the Spitzer, WISE, and Herschel missions showed that the planet-forming material in the disk is made up pebble-size grains of olivine. Olivine is one of the most abundant silicates in Earth’s mantle.

“The three rings around this young star are nested like Russian dolls and undergoing dramatic changes reminiscent of planetary formation,” said Mawet. “We have shown that silicate grains have agglomerated into pebbles, which are the building blocks of planet embryos.”

These images and studies are just the beginning for the vortex coronagraph. It will be used to look at many more young planetary systems. In particular, it will look at planets near so-called ‘frost lines’ in other solar systems. The is the region around star systems where it’s cold enough for molecules like water, methane, and carbon dioxide to condense into solid, icy grains. Current thinking says that the frost line is the dividing line between where rocky planets and gas planets are formed. Astronomers hope that the coronagraph can answer questions about hot Jupiters and hot Neptunes.

Hot Jupiters and Neptunes are large gaseous planets that are found very close to their stars. Astronomers want to know if these planets formed close to the frost line then migrated inward towards their stars, because it’s impossible for them to form so close to their stars. The question is, what forces caused them to migrate inward? “With a bit of luck, we might catch planets in the process of migrating through the planet-forming disk, by looking at these very young objects,” Mawet said.

Posted on by Nancy Atkinson

Unprecedented Views of Saturn’s Rings as Cassini Dances Death Spiral

This image shows a region in Saturn's outer B ring. NASA's Cassini spacecraft viewed this area at a level of detail twice as high as it had ever been observed before. And from this view, it is clear that there are still finer details to uncover. Credit: NASA/JPL-Caltech/Space Science Institute

As the Cassini spacecraft moves ever closer to Saturn, new images provide some of the most-detailed views yet of the planet’s spectacular rings. From its “Ring-Grazing” orbit phase, Cassini’s cameras are resolving details in the rings as small as 0.3 miles (550 meters), which is on the scale of Earth’s tallest buildings.

On Twitter, Cassini Imaging Team Lead Carolyn Porco called the images “outrageous, eye-popping” and the “finest Cassini images of Saturn’s rings.”

Project Scientist Linda Spilker said the ridges and furrows in the rings remind her of the grooves in a phonograph record.

These images are giving scientists the chance to see more details about ring features they saw earlier in the mission, such as waves, wakes, and things they call ‘propellers’ and ‘straw.’

This Cassini image features a density wave in Saturn’s A ring (at left) that lies around 134,500 km from Saturn. Density waves are accumulations of particles at certain distances from the planet. This feature is filled with clumpy perturbations, which researchers informally refer to as “straw.” Credit: NASA/JPL-Caltech/Space Science Institute

As of this writing, Cassini just started the 10th orbit of the 20-orbit ring-grazing phase, which has the spacecraft diving past the outer edge of the main ring system. The ring-grazing orbits began last November, and will continue until late April, when Cassini begins its grand finale. During the 22 finale orbits, Cassini will repeatedly plunge through the gap between the rings and Saturn. The first of these plunges is scheduled for April 26.

The spacecraft is actually close enough to the ‘F’ ring that occasionally tenuous particle strike Cassini, said project scientist Linda Spilker, during a Facebook Live event today.

“These are very small and tenuous, only a few microns in size,” Spilker said, “like dust particles you’d see in the sunlight. We can actually ‘hear’ them hitting the spacecraft in our data, but these particles are so small, they won’t hurt Cassini.”

I talked with Spilker about ring particles for my book “Incredible Stories From Space:”

Spilker has envisioned holding a ring particle in her hand. What would it look like?

“We have evidence of the particles that have an icy core covered with fluffy regolith material that is very porous,” she said, “and that means the particle can heat up and cool down very quickly compared to a solid ice cube.”

The straw features are caused by clumping ring particles and the propellers are caused by small, embedded moonlets that creates propeller shaped wakes in the rings.

The wavemaker moon, Daphnis, is featured in this view, taken as NASA’s Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn’s rings on Jan. 16, 2017. This is the closest view of the small moon obtained yet. Daphnis is 5 miles or 8 kilometers across. Credit: NASA/JPL-Caltech/Space Science Institute

This stunning view of the moon Daphnis shows the moon interacting with the ring particles, creating waves in the rings around it.

A close-up of Saturn and its rings. Assembled using raw uncalibrated RGB filtered images taken by the Cassini spacecraft on January 18 2017. Credit:
NASA/JPL-Caltech/SSI/image editing by Kevin M. Gill

“These close views represent the opening of an entirely new window onto Saturn’s rings, and over the next few months we look forward to even more exciting data as we train our cameras on other parts of the rings closer to the planet,” said Matthew Tiscareno, a Cassini scientist who studies Saturn’s rings at the SETI Institute, Mountain View, California. Tiscareno planned the new images for the camera team.

Further reading: JPL, CICLOPS