Cassini: A parcel of papers published

The Cassini spacecraft ended its mission on Sept. 15, 2017. Image Credit: NASA/JPL-Caltech/Space Science Institute
This natural-color view is a composite of images taken in visible light with the Cassini spacecraft’s narrow-angle camera at a distance of approximately 1.4 million miles (2.3 million kilometers) from Saturn. The Cassini spacecraft ended its mission on Sept. 15, 2017. Image Credit: NASA/JPL-Caltech/Space Science Institute

October 4, 2018 — New research emerging from the final orbits of NASA’s Cassini spacecraft represents a huge leap forward in our understanding of the Saturn system — especially the mysterious, never-before-explored region between the planet and its rings. Some preconceived ideas are turning out to be wrong while new questions are being raised.

Six teams of researchers are publishing their work Oct. 5 in the journal Science, based on findings from Cassini’s Grand Finale. That’s when, as the spacecraft was running out of fuel, the mission team steered Cassini spectacularly close to Saturn in 22 orbits before deliberately vaporizing it in a final plunge into the atmosphere in September 2017.

Knowing Cassini’s days were numbered, its mission team went for gold. The spacecraft flew where it was never designed to fly. For the first time, it probed Saturn’s magnetized environment, flew through icy, rocky ring particles and sniffed the atmosphere in the 1,200-mile-wide (2,000-kilometer-wide) gap between the rings and the cloud tops. Not only did the flight path push the spacecraft to its limits, the new findings illustrate how powerful and agile the instruments were.

Many more Grand Finale science results are to come, but here are some of today’s highlights:

  • Complex organic compounds embedded in water nanograins rain down from Saturn’s rings into its upper atmosphere. Scientists saw water and silicates, but they were surprised to see also methane, ammonia, carbon monoxide, nitrogen and carbon dioxide. The composition of the organics is different from that found on moon Enceladus — and also different from that on moon Titan, meaning there are at least three distinct reservoirs of organic molecules in the Saturn system.
  • For the first time, Cassini saw up close how rings interact with the planet and observed inner-ring particles and gases falling directly into the atmosphere. Some particles take on electric charges and spiral along magnetic-field lines, falling into Saturn at higher latitudes — a phenomenon known as “ring rain.” But scientists were surprised to see that others are dragged quickly into Saturn at the equator. And it’s all falling out of the rings faster than scientists thought — as much as 22,000 pounds (10,000 kilograms) of material per second.
  • Scientists were surprised to see what the material looks like in the gap between the rings and Saturn’s atmosphere. They knew that the particles throughout the rings ranged from large to small. But the sampling in the gap showed mostly tiny, nanometer-sized particles, like smoke, suggesting that some yet-unknown process is grinding up particles.
  • Saturn and its rings are even more interconnected than scientists thought. Cassini revealed a previously unknown electric-current system that connects the rings to the top of Saturn’s atmosphere.
  • Scientists discovered a new radiation belt around Saturn, close to the planet and composed of energetic particles. They found that while the belt actually intersects with the innermost ring, the ring is so tenuous that it doesn’t block the belt from forming.
  • Unlike every other planet with a magnetic field in our Solar System, Saturn’s magnetic field is almost completely aligned with its spin axis. The new data shows a magnetic-field tilt of less than 0.0095 degrees. (Earth’s magnetic field is tilted 11 degrees from its spin axis.) According to everything scientists know about how planetary magnetic fields are generated, Saturn should not have one. It’s a mystery that physicists will be working to solve.
  • Cassini flew above Saturn’s magnetic poles, directly sampling regions where radio emissions are generated. The findings more than doubled the number of direct measurements of radio sources from the planet, one of the few non-terrestrial locations where scientists have been able to study a radio-generation mechanism that is believed to operate throughout the universe.

For the Cassini mission, the science rolling out from Grand Finale orbits more than justifies the calculated risk of diving into the gap — skimming the upper atmosphere and skirting the edge of the inner rings, said Cassini Project Scientist Linda Spilker.

“Almost everything going on in that region turned out to be a surprise,” Spilker said. “That was the importance of going there, to explore a place we’d never been before. And the expedition really paid off — the data is tremendously exciting.”

Analysis of Cassini data from the spacecraft’s instruments will be ongoing for years to come, helping to paint a clearer picture of Saturn.

“Many mysteries remain, as we put together pieces of the puzzle,” Spilker said. “Results from Cassini’s final orbits turned out to be more interesting than we could have imagined.”

The papers published in Science are:

On Oct. 4, as the Science publication embargo lifts, articles describing research complementary to these findings will post online in Geophysical Research Letters (GRL), a journal of the American Geophysical Union (AGU).

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At Monday, August 13 meeting: Crewed American space missions: 2018

The program for the August 13 General Membership Meeting will cover American Crewed Space Missions: 2018. The talk will be delivered by Tom Benson, a retired NASA aerospace engineer.

SpaceX Falcon 9 - Credit: SpaceX

On July 8, 2011, the final Space Shuttle mission was launched from Cape Canaveral.

For the last six years, the United States has paid the Russian Space Agency to deliver crew members to the International Space Station (ISS). That process is about to end as Americans will once again ride on American spacecraft launched from U.S. soil!

The Commercial Crew Program of NASA has contracted with SpaceX and Boeing to each develop a spacecraft which can deliver and return astronauts to the ISS. The first flights are scheduled for this year. Tom Benson, retired from NASA Glenn Research Center, will report on these missions and share with us any breaking news from the “high frontier!”

The CAA’s monthly meetings are held on the second Monday of every month (except December) at 7:30 PM at the Rocky River Nature Center; 24000 Valley Parkway; North Olmsted, Ohio, in the Cleveland Metroparks.

Following the presentation and a brief social break, the club will conduct its membership business meeting.

Illustration: Falcon 9 booster with Dragon crewed spacecraft. Credit: SpaceX

Ancient organic material, mysterious methane on Mars

This low-angle self-portrait of NASA's Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called "Buckskin" on lower Mount Sharp. Image Credit: NASA/JPL-Caltech/MSSS
This low-angle self-portrait of NASA’s Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called “Buckskin” on lower Mount Sharp. Image Credit: NASA/JPL-Caltech/MSSS

From a NASA News Release

NASA’s Curiosity rover has found new evidence preserved in rocks on Mars that suggests the planet could have supported ancient life, as well as new evidence in the Martian atmosphere that relates to the search for current life on the Red Planet. While not necessarily evidence of life itself, these findings are a good sign for future missions exploring the planet’s surface and subsurface.

The new findings – “tough” organic molecules in three-billion-year-old sedimentary rocks near the surface, as well as seasonal variations in the levels of methane in the atmosphere – appear in the June 8 edition of the journal Science.

Organic molecules contain carbon and hydrogen, and also may include oxygen, nitrogen and other elements. While commonly associated with life, organic molecules also can be created by non-biological processes and are not necessarily indicators of life.

“With these new findings, Mars is telling us to stay the course and keep searching for evidence of life,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters, in Washington. “I’m confident that our ongoing and planned missions will unlock even more breathtaking discoveries on the Red Planet.”

“Curiosity has not determined the source of the organic molecules,” said Jen Eigenbrode of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who is lead author of one of the two new Science papers. “Whether it holds a record of ancient life, was food for life, or has existed in the absence of life, organic matter in Martian materials holds chemical clues to planetary conditions and processes.”

Although the surface of Mars is inhospitable today, there is clear evidence that in the distant past, the Martian climate allowed liquid water – an essential ingredient for life as we know it – to pool at the surface. Data from Curiosity reveal that billions of years ago, a water lake inside Gale Crater held all the ingredients necessary for life, including chemical building blocks and energy sources.

“The Martian surface is exposed to radiation from space. Both radiation and harsh chemicals break down organic matter,” said Eigenbrode. “Finding ancient organic molecules in the top five centimeters of rock that was deposited when Mars may have been habitable, bodes well for us to learn the story of organic molecules on Mars with future missions that will drill deeper.”

Seasonal Methane Releases

In the second paper, scientists describe the discovery of seasonal variations in methane in the Martian atmosphere over the course of nearly three Mars years, which is almost six Earth years. This variation was detected by Curiosity’s Sample Analysis at Mars (SAM) instrument suite.

Water-rock chemistry might have generated the methane, but scientists cannot rule out the possibility of biological origins. Methane previously had been detected in Mars’ atmosphere in large, unpredictable plumes. This new result shows that low levels of methane within Gale Crater repeatedly peak in warm, summer months and drop in the winter every year.

“This is the first time we’ve seen something repeatable in the methane story, so it offers us a handle in understanding it,” said Chris Webster of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, lead author of the second paper. “This is all possible because of Curiosity’s longevity. The long duration has allowed us to see the patterns in this seasonal ‘breathing.'”

Finding Organic Molecules

To identify organic material in the Martian soil, Curiosity drilled into sedimentary rocks known as mudstone from four areas in Gale Crater. This mudstone gradually formed billions of years ago from silt that accumulated at the bottom of the ancient lake. The rock samples were analyzed by SAM, which uses an oven to heat the samples (in excess of 900 degrees Fahrenheit, or 500 degrees Celsius) to release organic molecules from the powdered rock.

SAM measured small organic molecules that came off the mudstone sample – fragments of larger organic molecules that don’t vaporize easily. Some of these fragments contain sulfur, which could have helped preserve them in the same way sulfur is used to make car tires more durable, according to Eigenbrode.

The results also indicate organic carbon concentrations on the order of 10 parts per million or more. This is close to the amount observed in Martian meteorites and about 100 times greater than prior detections of organic carbon on Mars’ surface. Some of the molecules identified include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.

In 2013, SAM detected some organic molecules containing chlorine in rocks at the deepest point in the crater. This new discovery builds on the inventory of molecules detected in the ancient lake sediments on Mars and helps explains why they were preserved.

Finding methane in the atmosphere and ancient carbon preserved on the surface gives scientists confidence that NASA’s Mars 2020 rover and ESA’s (European Space Agency’s) ExoMars rover will find even more organics, both on the surface and in the shallow subsurface.

These results also inform scientists’ decisions as they work to find answers to questions concerning the possibility of life on Mars.

“Are there signs of life on Mars?” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program, at NASA Headquarters. “We don’t know, but these results tell us we are on the right track.”

This work was funded by NASA’s Mars Exploration Program for the agency’s Science Mission Directorate (SMD) in Washington. Goddard provided the SAM instrument. JPL built the rover and manages the project for SMD.

Want to see Wednesday’s total lunar eclipse? TV or online are best bet!

Photo: Umbral Shadow Crossing Moon by James Guilford
Umbral Shadow Crossing Moon by James Guilford

A total lunar eclipse will take place in the pre-dawn hours of January 31 but interested viewers in Northeastern Ohio are not well-favored! Weather conditions predicted for Wednesday morning are poor (mostly cloudy, at best) and the timing of the eclipse event itself works against us; at best we would see only a portion of the partial phase before our Moon sets!

Our best bet for watching this total lunar eclipse will be to view it on television or via streaming video. NASA Television and the agency’s website will provide live coverage of the celestial spectacle beginning at 5:30 a.m. EST. Weather permitting, the broadcast will feature views from the varying vantage points of telescopes at NASA’s Armstrong Flight Research Center in Edwards, California; Griffith Observatory in Los Angeles; and the University of Arizona’s Mt. Lemmon SkyCenter Observatory. You can access the live NASA broadcast via some cable television services, or online through NASA’s Moon webpages.

If skies do clear enough to see the Moon from our area, here’s a timetable for significant points in the upcoming eclipse as viewed from the city of Oberlin — the timing would be off only by a few seconds viewed from other areas of Northeastern Ohio.

Timetable of January 31, 2018 Total Lunar Eclipse. Credit: TimeAndDate.com
Timetable of January 31, 2018 Total Lunar Eclipse. Credit: TimeAndDate.com

This eclipse event is getting special attention because it offers the rare coincidence of three lunar events: A “supermoon,” a “blue moon” and a total lunar eclipse at the same time. A “supermoon” occurs when the Moon is closest to Earth in its orbit (at or near perigee) and appears about 14 percent brighter than usual. As the second Full Moon of the month, this Moon is also commonly called a Blue Moon, though it will not be blue in appearance. The “Super Blue Moon” will pass through Earth’s shadow and take on a reddish copper to deep-red tint. The eerie colors of totality seen during lunar eclipses frightened the ancients but delight us!

The last total lunar eclipse occurred Sept. 27-28, 2015. The next total lunar eclipse visible across North America will occur January 21, 2019.

The January 31 eclipse is the third in a series of supermoons in December 2017 and January 2018. Watch the Supermoon Trilogy video.

November 13: Monthly Membership Meeting

Artist's Concept: Nuclear Rocket at Mars. Credit: NASA
Artist’s Concept: Nuclear Rocket at Mars. Credit: NASA

The Cuyahoga Astronomical Association (CAA) will host its monthly meeting at 7:30 PM, Monday, November 13 in the Cleveland Metroparks’ Rocky River Nature Center, North Olmsted. Our speaker, Dr. Stanley Borowski, a Senior Engineer at NASA’s Glenn Research Center, Cleveland, will discuss the use of nuclear rocket engines in space exploration. The program is free and open to the public, no reservations required.

Following the program, the club’s monthly membership meeting will convene.

First observation of gravitational wave source, a kilonova: the merger of two neutron stars

Photo: Kilonova observed. Credit: NASA and ESA. Acknowledgment: A.J. Levan (U. Warwick), N.R. Tanvir (U. Leicester), and A. Fruchter and O. Fox (STScI)
On 17 August 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Interferometer both detected gravitational waves from the collision between two neutron stars. Within 12 hours observatories had identified the source of the event within the lenticular galaxy NGC 4993, shown in this image gathered with the NASA/ESA Hubble Space Telescope. The associated stellar flare, a kilonova, is clearly visible in the Hubble observations. This is the first time the optical counterpart of a gravitational wave event was observed. Hubble observed the kilonova gradually fading over the course of six days, as shown in these observations taken in between 22 and 28 August. Credit: NASA and ESA. Acknowledgment: A.J. Levan (U. Warwick), N.R. Tanvir (U. Leicester), and A. Fruchter and O. Fox (STScI)

On 17 August 2017 the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Interferometerboth alerted astronomical observers all over the globe about the detection of a gravitational wave event named GW170817. About two seconds after the detection of the gravitational wave, ESA’s INTEGRAL telescope and NASA’s Fermi Gamma-ray Space Telescope observed a short gamma-ray burst in the same direction.

In the night following the initial discovery, a fleet of telescopes started their hunt to locate the source of the event. Astronomers found it in the lenticular galaxy NGC 4993, about 130 million light-years away. A point of light was shining where nothing was visible before and this set off one of the largest multi-telescope observing campaigns ever — among these telescopes was the NASA/ESA Hubble Space Telescope.

Several different teams of scientists used Hubble over the two weeks following the gravitational wave event alert to observe NGC 4993. Using Hubble’s high-resolution imaging capabilities they managed to get the first observational proof for a kilonova, the visible counterpart of the merging of two extremely dense objects — most likely two neutron stars. Such mergers were first suggested more than 30 years ago but this marks the first firm observation of such an event. The distance to the merger makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen.

“Once I saw that there had been a trigger from LIGO and Virgo at the same time as a gamma-ray burst I was blown away,” recalls Andrew Levan of the University of Warwick, who led the Hubble team that obtained the first observations. “When I realised that it looked like neutron stars were involved, I was even more amazed. We’ve been waiting a long time for an opportunity like this!”

Hubble captured images of the galaxy in visible and infrared light, witnessing a new bright object within NGC 4993 that was brighter than a nova but fainter than a supernova. The images showed that the object faded noticeably over the six days of the Hubble observations. Using Hubble’s spectroscopic capabilities the teams also found indications of material being ejected by the kilonova as fast as one-fifth of the speed of light.

“It was surprising just how closely the behaviour of the kilonova matched the predictions,” said Nial Tanvir, professor at the University of Leicester and leader of another Hubble observing team. “It looked nothing like known supernovae, which this object could have been, and so confidence was soon very high that this was the real deal.”

Connecting kilonovae and short gamma-ray bursts to neutron star mergers has so far been difficult, but the multitude of detailed observations following the detection of the gravitational wave event GW170817 has now finally verified these connections.

“The spectrum of the kilonova looked exactly like how theoretical physicists had predicted the outcome of the merger of two neutron stars would appear,” says Levan. “It ties this object to the gravitational wave source beyond all reasonable doubt.”

The infrared spectra taken with Hubble also showed several broad bumps and wiggles that signal the formation of some of the heaviest elements in nature. These observations may help solve another long-standing question in astronomy: the origin of heavy chemical elements, like gold and platinum. In the merger of two neutron stars, the conditions appear just right for their production.

The implications of these observations are immense. As Tanvir explains: “This discovery has opened up a new approach to astronomical research, where we combine information from both electromagnetic light and from gravitational waves. We call this multi-messenger astronomy — but until now it has just been a dream!”

Levan concludes: “Now, astronomers won’t just look at the light from an object, as we’ve done for hundreds of years, but also listen to it. Gravitational waves provide us with complementary information from objects which are very hard to study using only electromagnetic waves. So pairing gravitational waves with electromagnetic radiation will help astronomers understand some of the most extreme events in the Universe.”

Monday, September 11: Monthly Membership Meeting

Image: Artist's concept of Cassini spacecraft at Saturn. Credit: NASA/JPL-Caltech
In this still from the short film Cassini’s Grand Finale, the spacecraft is shown diving between Saturn and the planet’s innermost ring. Credit: NASA/JPL-Caltech

The Cuyahoga Astronomical Association (CAA) will host its monthly meeting at 7:30 PM, Monday, September 11 in the Cleveland Metroparks’ Rocky River Nature Center, North Olmsted. The speaker will be Jay Reynolds who will discuss NASA’s Cassini Mission to Saturn and its finale, set to occur September 15. The program is free and open to the public, no reservations required.

The Cassini spacecraft will make its final approach to the giant planet Saturn this Friday, ending an extremely productive seven-year mission. This encounter will be like no other. This time, Cassini will dive into the planet’s atmosphere, sending science data for as long as its small thrusters can keep the spacecraft’s antenna pointed at Earth. Soon after, Cassini will burn up and disintegrate like a meteor.

In addition to being a research astronomer who teaches at Cleveland State University, Reynolds is CAA’s observatory director. He frequently appears on Cleveland television, hosting a show about astronomy on WKYC, Channel 3.

Following the program, the club’s monthly membership meeting will convene.