Astronomy Archives

October 16, 2014December 23, 2015 by Shannon Hall

Distant Galaxies Reveal 3D Cosmic Web for the First Time

3D map of the cosmic web at a distance of 10.8 billion light years from Earth. The map was generated from imprints of hydrogen gas observed in the spectrum of 24 background galaxies, which are located behind the volume being mapped. This is the first time that large-scale structures in such a distant part of the Universe have been mapped directly. The coloring represents the density of hydrogen gas tracing the cosmic web, with brighter colors representing higher density. Credit: Casey Stark (UC Berkeley) and Khee-Gan Lee (MPIA)

On the largest scales, networks of gaseous filaments span hundreds of millions of light-years, connecting massive galaxy clusters. But this gas is so rarified, it’s impossible to see directly.

For years, astronomers have used quasars — brilliant galactic centers fueled by supermassive black holes rapidly accreting material — to map the otherwise invisible matter.

But now, for the first time, a team of astronomers led by Khee-Gan Lee, a post-doc at the Max Planck Institute for Astronomy, has managed to create a three-dimensional map of the large-scale structure of the Universe using distant galaxies. And the advantages are numerous.

The science has always gone a little something like this: as the bright light from a distant quasar travels toward Earth, it encounters the intervening clouds of hydrogen gas and is partially absorbed. This leaves dark absorption lines in the quasar’s spectrum.

Artist's impression illustrating the technique of Lyman-alpha tomography: as light from distant background galaxies (yellow arrows) travels through the Universe towards Earth, hydrogen gas in the foreground leaves a characteristic imprint ("absorption signature"). From this imprint, astronomers can reconstruct which clouds the light has encountered as it traverses the "cosmic web" of dark matter and gas that accounts for the biggest structures in our universe. By observing a number of background galaxies in a small patch of the sky, astronomers were able to create a 3D map of the cosmic web using a technique similar to medical computer tomography (CT) scans. The coloring represents the density of hydrogen gas tracing the cosmic web, with brighter colors representing higher density. The rendition of the cosmic web in this image is based on a supercomputer simulation of cosmic structure formation. Credit: Khee-Gan Lee (MPIA) and Casey Stark (UC Berkeley) — Artist’s impression illustrating how a distant quasar’s or galaxy’s spectrum becomes clouded with absorption lines from intervening hydrogen gas. Credit: Khee-Gan Lee (MPIA) and Casey Stark (UC Berkeley)

If the Universe were static, the dark absorption lines would always be located at the same spot (121 nanometers for the so-called Lyman-alpha line) in the quasar’s spectrum. But because the Universe is expanding, the distant quasar is flying away from the Earth at a rapid speed. This stretches the quasar’s light, such that each intervening hydrogen gas cloud imprints its absorption signature on a different region of the quasar’s spectrum, leaving a forest of lines.

Therefore detailed measurements of multiple quasars’ spectra close together can actually reveal the three-dimensional nature of the intervening hydrogen clouds. But galaxies are nearly 100 times more numerous than quasars. So in theory they should provide a much more detailed map.

The only problem is that galaxies are also about 15 times fainter than quasars. So astronomers thought they were simply not bright enough to see well in the distant universe. But Lee carried out calculations that suggested otherwise.

“I was surprised to find that existing large telescopes should already be able to collect sufficient light from these faint galaxies to map the foreground absorption, albeit at a lower resolution than would be feasible with future telescopes,” said Lee in a news release. “Still, this would provide an unprecedented view of the cosmic web which has never been mapped at such vast distances.”

Lee and his colleagues used the 10-meter Keck I telescope on Mauna Kea, Hawaii to take a look a closer look at the distant galaxies and the forest of hydrogen absorption embedded in their spectra. But even the weather in Hawaii can turn ugly.

“We were pretty disappointed as the weather was terrible and we only managed to collect a few hours of good data,” said coauthor Joseph Hennawi, also from the Max Planck Institute for Astronomy. “But judging by the data quality as it came off the telescope, it was already clear to me that the experiment was going to work.”

The team was only able to collect data for four hours. But it was still unprecedented. They looked at 24 distant galaxies, which provided sufficient coverage of a small patch of the sky and allowed them to combine the information into a three-dimensional map.

The map reveals the large-scale structure of the Universe when it was only a quarter of its current age. But the team hopes to soon parse the map for more information about the structure’s function — following the flows of cosmic gas as it funneled away from voids and onto distant galaxies. It will provide a unique historical record on how the galaxy clusters and voids grew from inhomogeneities in the Big Bang.

The results have been published in the Astrophysical Journal and are available online.

October 16, 2014December 23, 2015 by Paul Patton

Moons of Confusion: Why Finding Extraterrestrial Life may be Harder than we Thought

NASA's James Webb Space Telescope, scheduled for launch in Dec. 2021, will be capable of measuring the spectrum of the atmospheres of Earthlike exoplanets orbiting small stars. Credit: NASA, Northrop Grumman

Astronomers and planetary scientists thought they knew how to find evidence of life on planets beyond our Solar System. But, a new study indicates that the moons of extrasolar planets may produce “false positives” adding an inconvenient element of uncertainty to the search.

More than 1,800 exoplanets have been confirmed to exist so far, with the count rising rapidly. About 20 of these are deemed potentially habitable. This is because they are only somewhat more massive than Earth, and orbit their parent stars at distances that might allow liquid water to exist.

Astronomers soon hope to be able to determine the composition of the atmospheres of such promising alien worlds. They can do this by analyzing the spectrum of light absorbed by them. For Earth-like worlds circling small stars, this challenging feat can be accomplished using NASA’s James Webb Space Telescope, scheduled for launch in 2018.

They thought they knew how to look for the signature of life. There are certain gases which shouldn’t exist together in an atmosphere that is in chemical equilibrium. Earth’s atmosphere contains lots of oxygen and trace amounts of methane. Oxygen shouldn’t exist in a stable atmosphere. As anyone with rust spots on their car knows, it has a strong tendency to combine chemically with many other substances. Methane shouldn’t exist in the presence of oxygen. When mixed, the two gases quickly react to form carbon dioxide and water. Without some process to replace it, methane would be gone from our air in a decade.

On Earth, both oxygen and methane remain present together because the supply is constantly replenished by living things. Bacteria and plants harvest the energy of sunlight in the process of photosynthesis. As part of this process water molecules are broken into hydrogen and oxygen, releasing free oxygen as a waste product. About half of the methane in Earth’s atmosphere comes from bacteria. The rest is from human activities, including the growing of rice, the burning of biomass, and the flatulence produced by the vast herds of cows and other ruminants maintained by our species.

By itself, finding methane in a planet’s atmosphere isn’t surprising. Many purely chemical processes can make it, and it is abundant in the atmospheres of the gas giant planets Jupiter, Saturn, Uranus, and Neptune, and on Saturn’s large moon Titan. Although oxygen alone is sometimes touted as a possible biomarker; its presence, by itself, isn’t rock solid evidence of life either. There are purely chemical processes that might make it on an alien planet, and we don’t yet know how to rule them out. Finding these two gases together, though, seems as close as one could get to “smoking gun” evidence for the activities of life.

A monkey wrench was thrown into this whole argument by an international team of investigators led by Dr. Hanno Rein of the Department of Environmental and Physical Sciences at the University of Toronto in Canada. Their results were published in the May, 2014 edition of the Proceedings of the National Academy of Sciences USA.

Suppose, they posited, that oxygen is present in the atmosphere of a planet, and methane is present separately in the atmosphere of a moon orbiting the planet. The team used a mathematical model to predict the light spectrum that might be measured by a space telescope near Earth for plausible planet-moon pairs. They found that the resulting spectra closely mimicked that of a single object whose atmosphere contained both gasses.

Unless the planet orbits one of the very nearest stars, they showed it wasn’t possible to distinguish a planet-moon pair from a single object using technology that will be available anytime soon. The team termed their results “inconvenient, but unavoidable…It will be possible to obtain suggestive clues indicative of possible inhabitation, but ruling out alternative explanations of these clues will probably be impossible for the foreseeable future.”

References and further reading:

The Habitable Exoplanets Catalog, Planetary Habitability Laboratory, University of Puerto Rico at Arecibo

Kaltenegger L., Selsis F., Fridlund M. et al. (2010) Deciphering spectral fingerprints of habitable exoplanets. Astrobiology, 10(1) p. 89-102.

Major J. (2013) Earthlike exoplanets are all around us. Universe Today

Rein H., Fujii Y., and Spiegel D. S. (2014) Some inconvenient truths about biosignatures involving two chemical species on Earth-like exoplanets. Proceedings of the National Academy of Sciences, 111(19) p. 6871-6875.

Sagan C., Thompson W. R., Carlson R., Gurnett, D., Hord, C. (1993) A search for life on Earth from the Galileo spacecraft. Nature, 365 p. 715-721.

October 16, 2014December 23, 2015 by Shannon Hall

MAVEN Spacecraft’s First Look at Mars Hints at Promising Results

Three views of an escaping atmosphere, obtained by MAVEN’s Imaging Ultraviolet Spectrograph. By observing all of the products of water and carbon dioxide breakdown, MAVEN's remote sensing team can characterize the processes that drive atmospheric loss on Mars. Image Credit: University of Colorado/NASA

It’s been less than a month since NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft slipped into orbit. But it’s already provided mission scientists their first look at Mars’ tenuous atmosphere.

“Everything is performing well so far,” said Bruce Jakosky, the mission’s principle investigator, in a news release. “All the instruments are showing data quality that is better than anticipated at this early stage of the mission. The spacecraft is performing beautifully. It’s turning out to be an easy and straightforward spacecraft to fly, at least so far. It really looks as if we’re headed for an exciting science mission.”

Data collected by MAVEN will answer a longstanding puzzle among planetary scientists. There’s ample evidence that early in the Red Planet’s history it had a much denser atmosphere. Rain fell from the sky and water carved its surface. But then the atmosphere vanished, and scientists are unsure why.

One leading theory is that the gas escaped to space, stripped away by the solar wind rushing past. (Click here to see a cool animation of that process.) Here on Earth, our magnetosphere helps protect our atmosphere from the solar wind. But once Mars lost its own magnetosphere, billions of years ago, its atmosphere became vulnerable.

MAVEN’s spectrometers will attempt to determine if hydrogen atoms, torn from water molecules by ultraviolet sunlight, are escaping to space and at what rate. Already, the spacecraft has observed the edges of the Martian atmosphere using its Imaging Ultraviolet Spectrograph (IUVS) camera, which is sensitive to the sunlight reflected by the atoms.

“With these observations, MAVEN’s IUVS has obtained the most complete picture of the extended Martian upper atmosphere ever made,” said team member Mike Chaffin from Colorado University at Boulder.

So far scientists have used IUVS to create a map of Mars’ ozone. “With these maps we have the kind of complete and simultaneous coverage of Mars that is usually only possible for Earth,” said team member Justin Deighan, also from CU-Boulder.

There will be about two weeks of additional instrument calibration and testing before MAVEN starts its primary science mission in early to mid-November. It will then likely take a few additional months to build up enough measurements to have a clear sense of what’s going on. But the initial results are promising.

October 15, 2014December 23, 2015 by Tim Reyes

Old Equations Shed New Light on Quasars

An artists illustration of the early Universe. Image Credit: NASA

There’s nothing more out of this world than quasi-stellar objects or more simply – quasars. These are the most powerful and among the most distant objects in the Universe. At their center is a black hole with the mass of a million or more Suns. And these powerhouses are fairly compact – about the size of our Solar System. Understanding how they came to be and how — or if — they evolve into the galaxies that surround us today are some of the big questions driving astronomers.

Now, a new paper by Yue Shen and Luis C. Ho – “The diversity of quasars unified by accretion and orientation” in the journal Nature confirms the importance of a mathematical derivation by the famous astrophysicist Sir Arthur Eddington during the first half of the 20th Century, in understanding not just stars but the properties of quasars, too. Ironically, Eddington did not believe black holes existed, but now his derivation, the Eddington Luminosity, can be used more reliably to determine important properties of quasars across vast stretches of space and time.

A quasar is recognized as an accreting (meaning- matter falling upon) super massive black hole at the center of an “active galaxy”. Most known quasars exist at distances that place them very early in the Universe; the most distant is at 13.9 billion light years, a mere 770 million years after the Big Bang. Somehow, quasars and the nascent galaxies surrounding them evolved into the galaxies present in the Universe today. At their extreme distances, they are point-like, indistinguishable from a star except that the spectra of their light differ greatly from a star’s. Some would be as bright as our Sun if they were placed 33 light years away meaning that they are over a trillion times more luminous than our star.

An artists illustration of the central engine of a Quasar. These "Quasi-stellar Objects" QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA) — An artists illustration of the central engine of a quasar. These “Quasi-stellar Objects” QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA)

The Eddington luminosity defines the maximum luminosity that a star can exhibit that is in equilibrium; specifically, hydrostatic equilibrium. Extremely massive stars and black holes can exceed this limit but stars, to remain stable for long periods, are in hydrostatic equilibrium between their inward forces – gravity – and the outward electromagnetic forces. Such is the case of our star, the Sun, otherwise it would collapse or expand which in either case, would not have provided the stable source of light that has nourished life on Earth for billions of years.

Generally, scientific models often start simple, such as Bohr’s model of the hydrogen atom, and later observations can reveal intricacies that require more complex theory to explain, such as Quantum Mechanics for the atom. The Eddington luminosity and ratio could be compared to knowing the thermal efficiency and compression ratio of an internal combustion engine; by knowing such values, other properties follow.

Several other factors regarding the Eddington Luminosity are now known which are necessary to define the “modified Eddington luminosity” used today.

The new paper in Nature shows how the Eddington Luminosity helps understand the driving force behind the main sequence of quasars, and Shen and Ho call their work the missing definitive proof that quantifies the correlation of a quasar properties to a quasar’s Eddington ratio.

They used archival observational data to uncover the relationship between the strength of the optical Iron [Fe] and Oxygen[O III] emissions – strongly tied to the physical properties of the quasar’s central engine – a super-massive black hole, and the Eddington ratio. Their work provides the confidence and the correlations needed to move forward in our understanding of quasars and their relationship to the evolution of galaxies in the early Universe and up to our present epoch.

Astronomers have been studying quasars for a little over 50 years. Beginning in 1960, quasar discoveries began to accumulate but only through radio telescope observations. Then, a very accurate radio telescope measurement of Quasar 3C 273 was completed using a Lunar occultation. With this in hand, Dr. Maarten Schmidt of California Institute of Technology was able to identify the object in visible light using the 200 inch Palomar Telescope. Reviewing the strange spectral lines in its light, Schmidt reached the right conclusion that quasar spectra exhibit an extreme redshift and it was due to cosmological effects. The cosmological redshift of quasars meant that they are at a great distance from us in space and time. It also spelled the demise of the Steady-State theory of the Universe and gave further support to an expanding Universe that emanated from a singularity – the Big Bang.

Dr. Maarten Schmidt, Caltech University, with Donald Lynden-Bell, were the first recipients of the Kavli Prize in Astrophysics, “for their seminal contributions to understanding the nature of quasars”. While in high school, this author had the privilege to meet Dr. Schmidt at the Los Angeles Museum of Natural History after his presentation to a group of students. (Photo Credit: Caltech) — Dr. Maarten Schmidt, Caltech, with Donald Lynden-Bell, were the first recipients of the Kavli Prize in Astrophysics, “for their seminal contributions to understanding the nature of quasars”. While in high school, this author had the privilege to meet Dr. Schmidt at the Los Angeles Museum of Natural History after his presentation to a group of students. (Photo Credit: Caltech)

The researchers, Yue Shen and Luis C. Ho are from the Institute for Astronomy and Astrophysics at Peking University working with the Carnegie Observatories, Pasadena, California.

References and further reading:

“The diversity of quasars unified by accretion and orientation”, Yue Shen, Luis C. Ho, Sept 11, 2014, Nature

“What is a Quasar?”, Universe Today, Fraser Cain, August 12, 2013

“Interview with Maarten Schmidt”, Caltech Oral Histories, 1999

“Fifty Years of Quasars, a Symposium in honor of Maarten Schmidt”, Caltech, Sept 9, 2013

October 15, 2014December 23, 2015 by Shannon Hall

Retired Astronaut Chris Hadfield Releases Stunning Space Photos

On a clear day, astronauts aboard the ISS can see over 1,000 miles from Havana to Washington D.C. Image Credit: Chris Hadfield / NASA

Orbiting 200 miles above the Earth, Retired Astronaut Chris Hadfield could easily photograph the ridges of the Himalayan Mountains, the textures of the Sahara Desert and the shadows cast by the tallest buildings in Manhattan.

The Richat Structure in Mauritania, also known as the Eye of the Sahara, is a landmark for astronauts. It’s hard to know where you are, especially if you’re over a vast 3,600,000-square-mile desert, but this bull’s-eye orients you, instantly. Oddly, it appears not to be the scar of a meteorite but a deeply eroded dome, with a rainbow-inspired color scheme. Image Credit: Chris Hadfield / NASA — Mauritania, also known as the Eye of the Sahara, is a landmark in the vast 3,600,000-square-mile desert. Credit: Chris Hadfield / NASA

“The view of the world when you have it just right there through the visor of your helmet is overpoweringly gorgeous,” said Hadfield, speaking Oct. 14 at the American Museum of Natural History in New York City. “It is phenomenal. The world is pouring by with all its colors and textures so fast.”

Although Hadfield has already shared many of his photos via social media, he unveiled another 150 images in his latest book, “You Are Here: Around The World in 92 Minutes.” The photographs open a rare window onto the Earth, illuminating our planet’s beauty and the consequences of human settlement.

The book is designed to replicate a single 92-minute orbit aboard the International Space Station. “It’s as if you and I are sitting at the window of the space station, and I said, ‘let’s go around the world once. I want to show you the really cool stuff,’ ” said Hadfield.

The astronaut, famed for his zero-gravity rendition of David Bowie’s “Space Oddity,” took approximately 45,000 photos during his 146-day stint on the space station in 2013. That’s roughly 300 photos per day every day. Since NASA does not set aside specific time slots for astronauts to take photos, Hadfield did so while he should have been asleep or serenading millions with his guitar.

The Himalayan mountain range in South Asia. Credit: Chris Hadfield / NASA

Why? Beauty triggers an unexplained emotional reaction, explained Hadfield. It also provides the best means of communication. Although the space station is an incredible scientific laboratory, art is equally important, he added, because it’s a way to reach people who might not otherwise be interested in the scientific nitty-gritty.

Hadfield is often attributed for humanizing space travel in a way that others before him had not. His use of social media, videos designed to quench our curiosity about living in space, and music, demonstrate a sheer passion that has inspired millions.

Manhattan awake at 9:23 a.m. local time, and Manhattan at rest at 3:45 a.m. local time. Image Credit: Chris Hadfield / NASA — Manhattan awake at 9:23 a.m. local time, and Manhattan at rest at 3:45 a.m. local time. Credit: Chris Hadfield / NASA

His photos not only share the natural beauty of our home planet, but also many signs of humanity, from bright city lights to the devastations of climate change as lakes dry up and disappear. “There’s so much information in just one glimpse out the window of human decision making and geology,” said Hadfield.

Hadfield’s remote yet vivid photos stand as a reminder of both the magnificence and fragility of life on our planet. “To have the world on one side, like this huge kaleidoscope, and then the bottomlessness of the Universe right there beside you,” said Hadfield, trailing off in awe. “You’re not on the world looking at it. You’re in the Universe with the world.”

October 15, 2014December 23, 2015 by Elizabeth Howell

Mars One Dustup: Founder Says Mission Won’t Fail As MIT Study Predicts

Artist's conception of Mars One human settlement. Credit: Mars One/Brian Versteeg

How possible is it to land humans on Mars? And can Mars One, the organization proposing to start with sending four astronauts one way, capable of doing it by 2025 as it promises?

A new study says that the Mars One concept could fail on several points: oxygen levels could skyrocket unsafely. Using the local resources to generate habitability is unproven. The technology is expensive. But the founder of Mars One says the Massachusetts Institute of Technology (MIT) student study is based on the wrong assumptions.

“It’s based on technology available on the ISS [International Space Station],” said Bas Landorp in an interview with Universe Today. “So you end up with a completely different Mars mission than Mars One. So their analysis has nothing to do with our mission.”

The mission has sparked a debate about sending humans on a trip with no promise for a return, but thousands of applicants vied for the chance to do it. After two cuts, the interim shortlist is now at 700 people. Those folks are awaiting interviews (more news is coming shortly, Landorp says) and no date has yet been announced for the next “cut.”

ISRO's Mars Orbiter Mission captures spectacular portrait of the Red Planet and swirling dust storms with the on-board Mars Color Camera from an altitude of 74500 km on Sept. 28, 2014. Credit: ISRO — ISRO’s Mars Orbiter Mission captures spectacular portrait of the Red Planet and swirling dust storms with the on-board Mars Color Camera from an altitude of 74500 km on Sept. 28, 2014. Credit: ISRO

A couple of weeks ago, MIT students presented a technical feasibility analysis of Mars One at the International Astronautical Congress in Toronto, Canada. The study is 35 pages long, so we recommend you read it to get the whole picture. The students’ main concerns are that crops (if they are responsible for 100% of the food) would send oxygen levels to unsafe margins, with no way to remove it. There are concerns with how well the in-situ resource utilization (using the resources on Mars to live off of) would perform. And the mission would cost $4.5 billion at a minimum — for the first crew only.

Cost: To get to Mars, the students say it will cost $4.5 billion and take 15 Falcon Heavy launches (a proposed next-generation rocket from SpaceX). Landorp says he can do it for $1.625 billion (since he doesn’t require constant Earth resupply) and as few as 13 launches (assuming $125 million per launch, a figure Landrop says is from SpaceX) by taking advantage of a few quirks of physics. If Mars One chooses a landing site that is four kilometers (2.5 miles) below the average Martian surface height, they will have both a thicker atmosphere and more time to land the payloads than, say, the Curiosity rover that landed about two kilometers (1.24 miles) above the average surface height. Mars One’s numbers show they could carry a payload of 2,500 kilograms (5,512 pounds) per mission, which they say is well within reach of what spacecraft can do today. The 13 launches would be divided into 11 robotic launches to send equipment to the surface, and two for humans (one to head to Earth orbit for assembly, and the other for the colonists to head to the in-orbit spacecraft and fly to Mars. The assembly crew would then fly back to Earth on the launch vehicle.)

Life support: While many of the technologies planned for use in life support are similar to those on the ISS — such as a trace gas system for air revitalization — Landorp says there will be some crucial differences. They are in talks with Paragon Space Systems Corp. (which describes itself as an environmental control firm for extreme environments, and whose customers include NASA and Bigelow.) As for the unsafe oxygen levels, Landorp points out there are plenty of oxygen removal systems available and that are used in hospitals and militaries. All that is needed is more testing in space. Landorp also points out these systems will be tested for two years robotically before humans land. “If that is not successful, then obviously we will not send humans,” he said.

The proposed Falcon Heavy rocket. Credit: SpaceX

In-situ resource utilization: Landorp acknowledges this requires more study, but says the robotic missions will be an important precursor for the human landings. Technologies needing to be developed will include nitrogen extraction from the Martian atmosphere. Oxygen production from water is well-studied in space, but water from the Martian surface (through vaporizing water in the soil) will require more work.

Another concern raised in media from time to time is where the money is coming from to fund Mars One. Landorp says right now funds are flowing from private investors. Mars One representatives are also in serious talks with a United Kingdom-based listed investment fund willing to finance the mission. In the long run, Landorp is confident money will come from broadcast deals similar to what partially fund the Olympics and the Fédération Internationale de Football Association (FIFA) competitions. Associated sponsorships would also help. But these won’t kick in until the colonists launch and land, since that’s when the world’s eyeballs will be on the mission.

Another stream of revenue, which may take five to seven years to kick in, will be intellectual property deals Mars One one representatives are working on closing now with potential suppliers, such as Lockheed Martin and Paragon. These agreements, should they go through as planned, would give Mars One a share of future revenue from any technologies flowing from the IP. “In the short term it’s not that interesting, it takes time to mature, but in the long term that will be interesting,” Landorp said.

October 15, 2014December 23, 2015 by David Dickinson

Comet A1 Siding Spring vs Mars: Views in Space and Time

Oh, to be a stranded astronaut on the surface of the planet Mars this week. There’s a great scene from Andy Weir’s recent novel The Martian where chief protagonist Mark Watney uses the swift moving moons of Phobos and Deimos to roughly gauge his direction while travelling across the expansive Martian desert.

This week, the skies over Mars will also be graced by an unforgettable and spectacular sight: the extremely close passage of Comet C/2013 A1 Siding Spring. The first comet discovered in 2013, A1 Siding Spring was spotted by veteran comet hunter Robert McNaught from the Siding Spring Observatory in Australia. Dozens of comets are discovered in any given year, but this one soon gained the attention of astronomers when it was found that the comet could possibly hit Mars in October 2014.

And although further observations refined A1 Siding Spring’s orbit and ruled out such an impact, the particulars of the close passage of the comet past Mars are still stunning: A1 Siding Spring will pass within 87,000 miles (139,500 kilometres) from the center of Mars on Sunday, October 19^th at 18:27 Universal Time (UT) or 2:27 PM EDT.

And although we’ve yet to set “boots” on Mars, a fleet of spacecraft arrayed throughout the inner solar system are set to study the comet from both near and far. NASA has taken measures to assure that spacecraft in orbit are afforded maximum protection from incoming cometary debris, and the exciting possibility exists that we’ll be able to study first-hand the interaction of the comet’s tail with the Martian atmosphere.

Credit NASA — Mars-based spacecraft set to observe Comet A1 Siding Spring: a scorecard. Credit: NASA.

Universe Today has written extensively on the scientific efforts to study the event, how to observe the comet from Earth, and the unprecedented amateur and professional campaign in progress to witness the close pass.

What we’d like to do now is imagine the unparalleled view under alien skies as the comet slides gracefully overhead.

The nucleus of A1 Siding Spring is thought to be 700 metres across, and the coma extends 19,300 km in diameter. The comet’s closest passage is just under six times the distance of Mars’ outer moon Deimos, and at closest approach, the coma will appear almost 8 degrees in size to any would-be Martian — that’s 16 times the diameter of a Full Moon as seen from the Earth — and will be crossing the skies at a staggering 1.5 degrees a minute. You would be able to easily see the motion of the comet as it moves across the Martian sky with the unaided (well, space suit helmet protected) eye after just a few dozen seconds worth of watching! The comet’s magnitude may reach -5 as seen from Mars, though that would also be extended over its huge expanded surface area.

The enormous tail of the comet would also span the sky, and NASA has already released several mind blowing simulations to this effect. We’ve also constructed some brief simulations using Starry Night that show the view of the encounter from Earth, Phobos, and the perspective from the comet itself:

There’s also been some discussion as of late that A1 Siding Spring has slowed down in terms of its predicted brightening, though this is not unusual or unexpected.

From Acidalia Planitia (the setting for The Martian) located in the mid-northern latitudes on the surface of Mars, the comet would be a fine morning object, sitting 48 degrees above the northeastern horizon at dawn at closest passage for one morning only, and perhaps staying visible even after sunrise. Earth would be in the picture too, shining at magnitude -2.5 in the Martian dawn.

And the view from the comet? Now that would be a truly spectacular ride, as Mars swells to 3 degrees in diameter as it approaches and recedes. The comet itself is on a million year plus orbit, never to again visit the realm of the inner solar system in our lifetimes.

Such a view has never been seen in recorded history from the Earth. The closest confirmed passage of a large comet near our planet was Comet D/1770 L1 Lexell, which passed over 15 times more distant than A1 Siding Spring from Mars, at 2.2 million km from Earth on July 1^st, 1770. Note that an even closer cometary passage in 1491 remains unverified. In more recent times, Comet Hyakutake passed 15.8 million km from Earth on March 25^th, 1996, with a tail that spanned half the sky as seen from a dark sky site, and long-time comet observers might also remember the 1983 passage of Comet IRAS-Araki-Alcock, which passed just 4.7 million kilometres from the Earth.

A1 Siding Spring imaged from Earth on October 11th, 2014. Credit: Efrain Morales Rivera.

And then there was the historic impact on Comet Shoemaker-Levy 9 into Jupiter in 1994, reminding us that cosmic catastrophes can and do indeed occur… the upper size limit estimate for the nucleus of A1 Siding Spring compares to 70% the size of Fragment G, and an impact on Earth or Mars of such a dirty snowball would be a very bad day, for rovers or the humans. An extinction level event such as the Chicxulub impactor, however, was estimated to be much larger, at about 10 km in size.

Thankfully, we’ve merely got a front row seat to the show this weekend, and our planet is not the main event. From Earth, Comet A1 Siding Spring will be a binocular object, shining at magnitude +9 as it passes 3’ from +0.9 magnitude Mars. Both will be visible briefly in dusk skies, and the Virtual Telescope Project also plans to broadcast the event live starting at 16:45 UT on October 19th.

Don’t miss the historic passage of Comet A1 Siding Spring past Mars… by this time next week, we fully expect more images of the comet — both amateur and professional — to grace the cyber-pages of Universe Today!

Imaging A1 Siding Spring and/or Mars? Send those astro-pics into Universe Today at our Flickr forum.

October 13, 2014December 23, 2015 by David Dickinson

Get Ready for the Fireballs of October

A recent fireball captured over the UK on October

On October 31^st 2005, trick-or-treaters across the central U.S. eastern seaboard were treated to a brilliant fireball, a celestial spectacle that frequently graces October skies.

Mid- to late October is fireball season, a time when several key meteor showers experience a broad peak. We’re already seeing an uptick in fireball activity as monitored by numerous all-sky cameras this month, including NASA’s system positioned across the United States. Three lesser known but fascinating showers are the chief culprits.

The main meteor shower on tap for the month of October is the Orionids. This shower radiates from the Club of the constellation Orion, and is the product of that most famous comet of them all, 1P Halley. Halley’s Comet is actually the source of two annual meteor showers, the October Orionids and the May Eta Aquarids. We’re seeing the inward stream of Halley debris in October, and Orionid velocities average a swift 66 kilometres a second. The radiant rides highest for northern hemisphere observers at 4 AM local, and 2014 sees an estimated zenithal hourly rate (ZHR) of 20 predicted to arrive on the mornings of October 21^st through the 22^nd. The Orionids experience a broad peak spanning October 21^st through November 7^th, and 2014 sees the peak arrive just two days prior to the Moon reaching New phase. The Orionids have exhibited an uptick in activity as high as 50-75 per hour from 2005-2007, and it’s been suggested that a 12 year peak cycle may govern the Orionids, as the path of meteoroid debris stream is modified by the gravitational influence of the giant planet Jupiter.

Two other nearby radiants in the sky also produce an exceptionally large number of fireballs in late October: the Southern Taurids and Northern Taurids. These are complex streams laid down by the periodic comet 2P Encke, which possesses the shortest orbital period of any comet known at 3.3 years. Though the ZHR for both is only slightly above the background sporadic rate for northern hemisphere Fall at about five per hour, the Taurids also produce a high ratio of fireballs. The southern Taurids peak in early October and are already active, and the Northern Taurids peak in late October through early November, earning them the nickname the “Fireballs of Halloween”. Unlike many meteor showers, the Northern Taurids are approaching the Earth from behind in our orbit and have a slow relative atmospheric entry velocity of 28 kilometres per second. This makes for long, stately meteor trains often visible in the evening hours before local midnight.

The Taurids also seem to exhibit a seven year periodicity that begs for further study. 2008 was a fine year for Taurid fireballs… could 2015 be next?

Of course, the exact definition of a “fireball” meteor varies by source, though we prefer the definition of a fireball as a meteor brighter than magnitude -3. A fireball reaching -14 (a Full Moon equals magnitude -13, about 2.5 times fainter) is often termed a bolide.

Halley's orbit — Comet 1P/Halley’s orbital path through the inner solar system. (Credit: NASA/JPL).

Observing meteor showers such as the Orionids is as simple as sitting back and patiently watching the skies. Our own personal rule while starting a meteor vigil is to scan the skies for 10 minutes; one or more meteor sightings is a good sign to keep on watching, while no meteors means it’s time to pack it in and instead maybe write about astronomy. Dark, moonless skies are key, and you can report how many meteors you see to the International Meteor Organization. Be sure to keep a pair of binoculars handy to examine any lingering smoke trails post-fireball passage.

The positions of the radiants of the Orionids and the Taurids, with peak dates. Credit: Stellarium.

Of course, seeing a Taurid fireball is largely a matter of luck and looking at the right place in the sky at the right time. All-sky cameras work great in this regard, and many amateurs now use tripod mounted DLSRs set to take wide-field exposures of the sky automatically throughout the night. Just watch out for dew! Nearly every meteor we’ve caught on camera turned up only in post review, a testament to how much of the sky a lone pair of eyes still misses.

Spot a fireball? The American Meteor Society maintains a great online database of recent sightings and reports. Keep in mind, lots of “meteor-wrongs” inevitably crop up on Facebook and Twitter during any event, posted by folks eager for likes and retweets. Faves of such spoofers are: the Peekskill meteor train, the reentry of Hyabusa, Mir, and scenes (!) from the movie Armageddon. We’ve seen ‘em all passed off as legit, though you’re more than welcome to try and be original… a majority of initial meteor images almost always come from dash cams (remember Chelyabinsk?) and security cameras.

Finally, in addition to fireballs, there’s another astronomical tie-in for Halloween, as it’s one of four cross-quarter tie-in days approximately mid-way between a solstice and an equinox. The other three are: Lammas Day (August 1st), Groundhog’s Day (February 2nd) and May Day (May 1^st). We just think that it’s great — if a bit paradoxical — to see modern day suburbanites dress up as ghouls and goblins as they reenact archaic rites and holidays…

Don’t forget to keep an eye out for the fireballs of October this Halloween!

October 13, 2014December 23, 2015 by Shannon Hall

A New Look at Dark Matter — Is the Milky Way Less of a Behemoth Than Previously Thought?

This annotated artist's conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA

Astronomy is notorious for raising more questions than it answers. Take the observation that the vast majority of matter is invisible.

Although astronomers have gathered overwhelming evidence that dark matter makes up roughly 84 percent of the universe’s matter — providing straightforward explanations for the rotation of individual galaxies, the motions of distant galaxy clusters, and the bending of distant starlight — they remain unsure about any specifics.

Now, a group of Australian astronomers thinks there’s only half as much dark matter in the Milky Way as previously thought.

In 1933, Swiss astronomer Fritz Zwicky observed the Coma cluster — a galaxy cluster roughly 320 million light-years away and nearly 2 light-years across — and found that it moved too rapidly. There simply wasn’t enough visible matter to hold the galaxy cluster together.

Zwicky decided there must be a hidden ingredient, known as dunkle Materie, or dark matter, that caused the motions of these galaxies to be so large.

The rotation curve of the Milky Way. Image Credit: Kafle et al.

Then in 1978, American astronomer Vera Rubin looked at individual galaxies. Astronomers largely assumed galaxies rotated much like our Solar System, with the outer planets rotating slower than the inner planets. This argument aligns with Newton’s Laws and the assumption that most of the mass is located in the center.

But Rubin found that galaxies rotated nothing like our own Solar System. The outer stars did not rotate slower than the inner stars, but just as fast. There had to be dark matter on the outskirts of every galaxy.

Now, astronomer Prajwal Kafle, from The University of Western Australia, and his colleagues have once again observed the speed of stars on the outskirts of our own galaxy, the Milky Way. But he did so in much greater detail than previous estimates.

From a star’s speed, it’s relatively simple to calculate any interior mass. The simple equation below shows that the interior mass (M) is equal to the distance the star is from the galactic center (R) times its velocity (V) squared, all divided by the gravitational constant (G):

Kafle and his colleagues used messier physics accounting for the sloppiness of the galaxy. But the point holds, with a star’s velocity, you can calculate any interior mass. And with multiple stars’ velocities you’re bound to be more accurate. The team found the dark matter in our galaxy weighs 800 billion times the mass of the Sun, half of previous estimates.

“The current idea of galaxy formation and evolution … predicts that there should be a handful of big satellite galaxies around the Milky Way that are visible with the naked eye, but we don’t see that,” said Kafle in a news release. This is typically referred to as the missing satellites problem, and it has evaded astronomers for years.

“When you use our measurement of the mass of the dark matter the theory predicts that there should only be three satellite galaxies out there, which is exactly what we see; the Large Magellanic Cloud, the Small Magellanic Cloud and the Sagittarius Dwarf Galaxy,” said Kafle.

These new measurements might prove the Milky Way is not quite the behemoth astronomers previously thought. They also help explain why there are so few satellite galaxies in orbit. But first the results will have to be confirmed as they stand up against numerous other ways to weigh the dark matter in our galaxy.

The results have been published in the Astrophysical Journal and are available online.

October 11, 2014December 23, 2015 by Jason Major

Watch the “Blood Moon” Eclipse from Mercury

Earth and the Moon imaged by the MESSENGER spacecraft on Oct. 8, 2014

Yes, it’s another time-lapse of the October 8 lunar eclipse that was observed by skywatchers across half the Earth… except that these images weren’t captured from Earth at all; this was the view from Mercury!

The animation above was constructed from 31 images taken two minutes apart by the MESSENGER spacecraft between 5:18 a.m. and 6:18 a.m. EDT on Oct. 8, 2014.

“From Mercury, the Earth and Moon normally appear as if they were two very bright stars,” said Hari Nair, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory, which developed and operates the MESSENGER mission for NASA. “During a lunar eclipse, the Moon seems to disappear during its passage through the Earth’s shadow, as shown in the movie.”

According to Nair the images have been zoomed by a factor of two and the Moon’s brightness has been increased by a factor of about 25 to enhance visibility. Captured by MESSENGER’s narrow-angle camera, Earth and the Moon were 0.713 AU (106.6 million km / 66.2 million miles) away from Mercury when the images were acquired.

Want to see some great photos of the eclipse shared by talented photographers around the world? Click here.

The Oct. 8 “Hunter’s Moon” eclipse was the second and last total lunar eclipse of 2014. The next will occur on April 4 of next year… but by that time MESSENGER won’t be around to witness it.

Launched August 3, 2004, MESSENGER entered orbit at Mercury on March 18, 2011. It is currently nearing the end of its missions as well as its its operational life, but we still have several more months of observations to look forward to from around the Solar System’s innermost planet before MESSENGER makes its final pass and ultimately impacts Mercury’s surface in March 2015.

Video credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Source: MESSENGER news release