Posted on by Matt Williams

The Hidden Glaciers Of Mars

Colour-coded topographic view of the Colles Nili region, showing the relative heights and depths of terrain. Credit: ESA/DLR/FU Berlin

In the northern hemisphere of Mars, between the planet’s southern highlands and the northern lowlands, is a hilly region known as Colles Nilli. This boundary-marker is a very prominent feature on Mars, as it is several kilometers in height and surrounded by the remains of ancient glaciers.

And thanks to the Mars Express mission, it now looks like this region is also home to some buried glaciers. Such was the conclusion after the orbiting spacecraft took images that revealed a series of eroded blocks along this boundary, which scientists have deduced are chunks of ice that became buried over time.

The Mars Express images show a plethora of these features along the north-south boundary. They also reveal several features that hint at the presence of buried ice and erosion – such as layered deposits as well as ridges and troughs. Similar features are also found in nearby impact craters. All of these are believed to have been caused by an ancient glacier as it retreated several hundred million years ago.

Artist's impression of the Mars Express spacecraft in orbit. Image Credit: ESA/Medialab
Artist’s impression of the Mars Express spacecraft in orbit. Credit: ESA/Medialab

It is further reasoned that these remaining ice deposits were covered by debris that was deposited from the plateau as it eroded. Wind-borne dust was also deposited over time, which is believed to be the result of volcanic activity. This latter source is evidenced by steaks of dark material deposited around the blocks, as well as dark sand dunes spotted within the impact craters.

Similar features are believed to exist within many boundary regions on Mars, and are believed to represent periods of glaciation that took place over the course of eons. And this is not the first time buried glaciers have been spotted on Mars.

For instance, back in 2008, the Mars Reconnaissance Orbiter (MRO) used its ground-penetrating radar to locate water ice under blankets or rocky debris, and at latitudes far lower than any that had been previously identified. At the time, this information shed light on a long-standing mystery about Mars, which was the presence of what are called “aprons”.

These gently-sloping rocky deposit, which are found at the bases of taller features, were first noticed by NASA’s Viking orbiters during the 1970s. A prevailing theory has been that these aprons are the result of rocky debris lubricated by small amounts of ice.

Artist's impression visualising the separation of the ExoMars entry, descent and landing demonstrator module, Schiaparelli, from the Trace Gas Orbiter (TGO). Credit: ESA
Artist’s impression of the separation of the ExoMars entry, descent and landing demonstrator module (Schiaparelli) from the Trace Gas Orbiter (TGO). Credit: ESA/ATG medialab

Combined with this latest info taken from the northern hemisphere, it would appear that there is plenty of ice deposits all across the surface of Mars. The presence (and prevalence) of these icy remnants offer insight into Mars’ geological past, which – like Earth – involved some “ice ages”.

The Mars Express mission has been actively surveying the surface of Mars since 2003. On October 19th, it will be playing a vital role as the Exomars mission inserts itself into Martian orbit and the Schiaparelli lander makes its descent and landing on the Martian surface.

Alongside the MRO and the ExoMars Orbiter, it will be monitoring signals from the lander to confirm its safe arrival, and will relay information sent from the surface during the course of its mission.

The ESA will be broadcasting this event live. And given that this mission will be the ESA’s first robotic lander to reach Mars, it should prove to be an exciting event!

Further Reading: ESA

Posted on by Matt Williams

The Universe’s Galaxy Population Just Grew Tenfold

New research indicates that there could be as many as 2 trillion galaxies in the known Universe. Credit: 2MASS/Caltech

Ever since human beings learned that the Milky Way was not unique or alone in the night sky, astronomers and cosmologists have sought to find out just how many galaxies there are in the Universe. And until recently, our greatest scientific minds believed they had a pretty good idea  – between 100 and 200 billion.

However, a new study produced by researchers from the UK has revealed something startling about the Universe. Using Hubble’s Deep Field Images and data from other telescopes, they have concluded that these previous estimates were off by a factor of about 10. The Universe, as it turns out, may have had up to 2 trillion galaxies in it during the course of its history.

Led by Prof. Christopher Conselice of the University of Nottingham, U.K., the team combined images taken by the Hubble Space Telescope with other published data to produced a 3-D map of the Universe. They then incorporated a series of new mathematical models that allowed them to infer the existence of galaxies which are not bright enough to be observed by current instruments.

Scientists believe they have found the missing matter of the universe, thus confirming our current cosmological models. Credit: NASA/Chandra
Scientists from the UK have produced new estimates on the number of galaxies in the Universe, which could shed light on cosmic evolution as well. Credit: NASA/Chandra

Using these, they then began reviewing how galaxies have evolved over the past 13 billion years. What they learned was quite fascinating. For one, they observed that the distribution of galaxies throughout the history of the Universe was not even. What’s more, they found that in order for everything in their calculations to add up, there had to be 10 times more galaxies in the early Universe than previously thought.

Most of these galaxies would be similar in mass to the satellite galaxies that have been observed around the Milky Way, and would be too faint to be spotted by today’s instruments. In other words, astronomers have only been able to see about 10% of the early Universe until now, because most of its galaxies were too small and faint to be visible.

As Prof. Conselice explained in a Hubble Science Release, while may help resolve a lingering debate about the structure of the Universe:

“These results are powerful evidence that a significant galaxy evolution has taken place throughout the universe’s history, which dramatically reduced the number of galaxies through mergers between them — thus reducing their total number. This gives us a verification of the so-called top-down formation of structure in the universe.”

Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. The goal of the Frontier Fields is to peer back further than the Hubble Ultra Deep Field and get a wealth of images of galaxies as they existed in the first several hundred million years after the Big Bang. Note that the unit of time is not linear in this illustration. Illustration Credit: NASA and A. Feild (STScI)
Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)

To break it down, the “top-down model” of galaxy formation states that galaxies formed from huge gas clouds larger than the resulting galaxies. These clouds began collapsing because their internal gravity was stronger than the pressures in the cloud. Based on the speed at which the gas clouds rotated, they would either form a spiral or an  elliptical galaxy.

In contrast, the “bottom-up model” states that galaxies formed during the early Universe due to the merging of smaller clumps that were about the size globular clusters. These galaxies could then have been drawn into clusters and superclusters by their mutual gravity.

In addition to helping to resolve this debate, this study also offers a possible solution to the Olbers’ Paradox (aka. “the dark night sky paradox”). Named after the 18th/19th century German astronomer Heinrich Wilhelm Olbers, this paradox addresses the question of why – given the expanse of the Universe and all the luminous matter in it – is the sky dark at night?

Based on their results, the UK team has surmised that while every point in the night sky contains part of a galaxy, most of them are invisible to the human eye and modern telescopes. This is due to a combination of factors, which includes the effects of cosmic redshift, the fact that the Universe is dynamic (i.e. always expanding) and the absorption of light by cosmic dust and gas.

Among other data, scientists used the galaxies visible in the Great Observatories Origins Deep Survey (GOODS) to recalculate the total number of galaxies in the observable Universe. The image was taken by the NASA/ESA Hubble Space Telescope and covers a portion of the southern field of GOODS. This is a large galaxy census, a deep-sky study by several observatories to trace the formation and evolution of galaxies.
Image was taken by the NASA/ESA Hubble Space Telescope which covers a portion of the southern field of Great Observatories Origins Deep Survey (GOODS). Credit: NASA/ESA/HST

Needless to say, future missions will be needed to confirm the existence of all these unseen galaxies. And in that respect, Conselice and his colleagues are looking to future missions – ones that are capable of observing stars and galaxies in the non-visible spectrum – to make that happen.

“It boggles the mind that over 90 percent of the galaxies in the universe have yet to be studied,” he added. “Who knows what interesting properties we will find when we discover these galaxies with future generations of telescopes? In the near future, the James Webb Space Telescope will be able to study these ultra-faint galaxies.”

Understanding how many galaxies have existed over time is a fundamental aspect of understanding the Universe as a whole. With every passing study that attempts to resolve what we can see with our current cosmological models, we are getting that much closer!

And be sure to enjoy this video about some of Hubble’s most stunning images, courtesy of HubbleESA:

Further Reading: HubbleSite, Hubble Space Telescope

Posted on by Bob King

We Land on Mars in Just 2 days!

Artist's view of the Schiaparelli lander descending to Mars on October 19. Credit: ESA


Watch how Schiaparelli will land on Mars. Touchdown will occur at 10:48 a.m. EDT (14:48 GMT) Wednesday Oct. 19.

Cross your fingers for good weather on the Red Planet on October 19. That’s the day the European Space Agency’s Schiaparelli lander pops open its parachute, fires nine, liquid-fueled thrusters and descends to the surface of Mars. Assuming fair weather, the lander should settle down safely on the wide-open plains of Meridiani Planum near the Martian equator northwest of NASA’s Opportunity rover. The region is rich in hematite, an iron-rich mineral associated with hot springs here on Earth.

On 19 October 2016, the ExoMars 2016 entry, descent, and landing demonstrator module, known as Schiaparelli, will land on Mars in a region known as Meridiani Planum. The landing sites of the seven rovers and landers that have reached the surface of Mars and successfully operated there are indicated on this map. The background image is a shaded relief map of Mars, based on data from the Mars Orbiter Laser Altimeter (MOLA) instrument, on NASA’s Mars Global Surveyor spacecraft.
On Wednesday, October 19, the ExoMars 2016 entry, descent and landing demonstrator module, named Schiaparelli, will land on Mars in Meridiani Planum not far from the Opportunity rover. The map shows the seven rovers and landers that have reached the surface of Mars and successfully operated there. The background image is a shaded relief map of Mars created using data from NASA’s Mars Global Surveyor spacecraft.

The 8-foot-wide probe will be released three days earlier from the Trace Gas Orbiter (TGO) and coast toward Mars before entering its atmosphere at 13,000 mph (21,000 km/hr). During the 6-minute-long descent, Schiaparelli will decelerate gradually using the atmosphere to brake its speed, a technique called aerobraking. Not only is Meridiani Planum flat, it’s low, which means the atmosphere is thick enough to allow Schiaparelli’s heat shield to reduce its speed sufficiently so the chute can be safely deployed. The final firing of its thrusters will ensure a soft and controlled landing.

Artist's impression depicting the separation of the ExoMars 2016 entry, descent and landing demonstrator module, named Schiaparelli, from the Trace Gas Orbiter, and heading for Mars. Credit: ESA/ATG medialab
Artist’s impression showing Schiaparelli separating from the Trace Gas Orbiter and heading for Mars. The lander is named for late 19th century Italian astronomer Giovanni Schiaparelli, who created a detailed telescopic map of Mars. The orbiter will sniff out potentially biological gases such as methane in Mars’ atmosphere and track its sources and seasonal variations. Credit: ESA/ATG medialab

The lander is one-half of the ExoMars 2016 mission, a joint venture between the European Space Agency and Russia’s Roscosmos. The Trace Gas Orbiter (TGO) will fire its thrusters to place itself in orbit about the Red Planet the same day Schiparelli lands. Its job is to inventory the atmosphere in search of organic molecules, methane in particular. Plumes of methane, which may be biological or geological (or both) in origin, have recently been detected at several locations on Mars including Syrtis Major, the planet’s most prominent dark marking. The orbiter will hopefully pinpoint the source(s) as well as study seasonal changes in locations and concentrations.

This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft, shows what appears to be a dust-covered frozen sea near the Martian equator. It shows a flat plain, part of the Elysium Planitia, that is covered with irregular blocky shapes. They look just like the rafts of fragmented sea ice that lie off the coast of Antarctica on Earth. Raised levels of methane were detected here by ESA's Mars Express orbiter. Copyright: ESA/DLR/FU Berlin (G. Neukum)
This image, taken by ESA’s Express spacecraft, shows what appears to be a dust-covered frozen sea near the Martian equator. Located in Elysium Planitia, the flat plain is covered with irregular blocky shapes. They look just like the rafts of fragmented sea ice that lie off the coast of Antarctica on Earth. Raised levels of methane were detected here by ESA’s Mars Express orbiter. Copyright: ESA/DLR/FU Berlin (G. Neukum)

Methane (CH4) has long been associated with life here on Earth. More than 90% of the colorless, odorless gas is produced by living organisms, primarily bacteria. Sunlight breaks methane down into other gases over a span of about 300 years. Because the gas relatively short-lived, seeing it on Mars implies an active, current source. There may be several:

  • Long-extinct bacteria that released methane that became trapped in ice or minerals in the upper crust. Changing temperature and pressure could stress the ice and release that ancient gas into today’s atmosphere.
  • Bacteria that are actively producing methane to this day.
  • Abiological sources. Iron can combine with oxygen in terrestrial hot springs and volcanoes to create methane. This gas can also become trapped in solid forms of water or ‘cages’ called clathrate hydrates that can preserve it for a long time. Olivine, a common mineral on Earth and Mars, can react with water under the right conditions to form another mineral called serpentine. When altered by heat, water and pressure, such in environments such as hydrothermal springs, serpentine can produce methane.

Will it turn out to be burping bacteria or mineral processes? Let’s hope TGO can point the way.

This image illustrates possible ways methane might get into Mars’ atmosphere and also be removed from it: microbes (left) under the surface that release the gas into the atmosphere, weathering of rock (right) and stored methane ice called a clathrate. Ultraviolet light can work on surface materials to produce methane as well as break it apart into other molecules (formaldehyde and methanol) to produce carbon dioxide. Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan
This image illustrates possible ways methane might get into Mars’ atmosphere and also be removed from it: microbes (left) under the surface that release the gas into the atmosphere, weathering of rock (right) and stored methane ice called a clathrate. Ultraviolet light can work on surface materials to produce methane as well as break it apart into other molecules (formaldehyde and methanol) to produce carbon dioxide. Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

The Trace Gas Orbiter will also use the Martian atmosphere to slow its speed and trim its orbital loop into a 248-mile-high (400 km) circle suitable for science observations. But don’t expect much in the way of scientific results right away; aerobraking maneuvers will take about a year, so TGO’s job of teasing out atmospheric ingredients won’t begin until December 2017. The study runs for 5 years.

The orbiter will also examine Martian water vapor, nitrogen oxides and other organics with far greater accuracy than any previous probe as well as monitor seasonal changes in the atmosphere’s composition and temperature. And get this — its instruments can map subsurface hydrogen, a key ingredient in both water and methane, down to a depth of a meter (39.4 inches) with greater resolution compared to previous studies. Who knows? We may discover hidden ice deposits or methane sinks that could influence where future rovers will land. Additional missions to Mars are already on the docket, including ExoMars 2020. More about that in a minute.

Schiaparelli, the
This artist’s view shows Schiaparelli, the entry, descent and landing demonstrator module, using its thrusters to make a soft landing on Mars on October 19 at 10:48 a.m. EDT (14:48 GMT). Credit: ESA/ATG medialab

While TGO’s mission will require years, the lander is expected to survive for only four Martian days (called ‘sols’) by using the excess energy capacity of its batteries. A set of scientific sensors will measure wind speed and direction, humidity, pressure and electric fields on the surface. A descent camera will take pictures of the landing site on the way down; we’ll should see those photos the very next day. Data and imagery from the lander will be transmitted to ESA’s Mars Express and a NASA Relay Orbiter, then relayed to Earth.


This animation shows the paths of the Trace Gas Orbiter and Schiaparelli lander on Oct. 19 when they arrive at Mars.

If you’re wondering why the lander’s mission is so brief, it’s because Schiaparelli is essentially a test vehicle. Its primary purpose is to test technologies for landing on Mars including the special materials used for protection against the heat of entry, a parachute system, a Doppler radar device for measuring altitude and liquid-fueled braking thrusters.

Martian dust storms can be cause for concern during any landing attempt. Since it’s now autumn in the planet’s northern hemisphere, a time when storms are common, there’s been some finger-nail biting of late. The good news is that storms of recent weeks have calmed and Mars has entered a welcome quiet spell.

To watch events unfold in real time, check out ESA’s live stream channel, Facebook page and Twitter updates. The announcement of the separation of the lander from the orbiter will be made around 11 a.m. Eastern Time (15:00 GMT) Sunday October 16.  Live coverage of the Trace Gas Orbiter arrival and Schiaparelli landing on Mars runs from 9-11:15 a.m. Eastern (13:00-15:15 GMT) on Wednesday October 19. Photos taken by Schiaparelli’s descent camera will be available starting at 4 a.m. Eastern (8:00 GMT) on October 20. More details here. We’ll also keep you updated on Universe Today.

The ExoMars 2016 mission will pave the way for a rover mission to the Red Planet in 2020. Credit: ESA
The ExoMars 2016 mission will pave the way for a rover mission to the Red Planet in 2020. Credit: ESA

Everything we learn during the current mission will be applied to planning and executing the next —  ExoMars 2020, slated to launch in 2020. That venture will send a rover to the surface to search and chemically test for signs of life, present or past.  It will collect samples with a drill at various depths and analyze the fines for bio-molecules. Getting down deep is important because the planet’s thin atmosphere lets through harsh UV light from the sun, sterilizing the surface.

Are you ready for adventure? See you on Mars (vicariously)!

Posted on by Matt Williams

An Exoplanet With Huge Rings Intrigues

Artist’s conception of the extrasolar ring system circling the young giant planet or brown dwarf J1407b. Credit: Ron Miller

Back in 2007, astronomers observed a series of unusual eclipses coming from a star 420 light years from Earth. In 2012, a team from Japan and the Netherlands reasoned that this phenomena was due to the presence of a large exoplanet – designated J1407b – with a massive ring system orbiting the star. Since then, several surprising finds have been made.

For example, in 2015, the same team concluded that the ring system is one-hundred times larger and heavier than Saturn’s (and may be similarly sculpted by exomoons). And in their most recent study, they have shown that these giant rings may last for over 100,000 years, assuming they have a rare and unusual orbit around their planet.

In their previous work, Rieder and Kenworth determined that the ring system around J1407b consisted about 37 rings that extend to a distance of 0.6 AU (90 million km) from the planet. They also estimated that these rings are 100 times as massive as our Moon – 7342 trillion trillion metric tons. What’s more, while J1407b’s existence is yet to be confirmed, they were able to rule out the possibility of it having a circular orbit around the star.

Giant Rings. The rings around J1407b are so large that we could see in the dusk from the earth when they were placed around the planet Saturn. The rings can be seen above the Old Leiden Observatory. Credit: M. Kenworthy / Leiden University
Artist’s impression of what the rings around J1407b would look like from Earth if they were placed around Saturn. The rings can be seen above the Old Leiden Observatory. Credit: M. Kenworthy / Leiden University

As a result, there were doubts that such a ring system could exist. Given the fact that the planet periodically gets closer to its star, the ring system would experience gravitational disruption. Therefore, Steven Rieder (of the RIKEN institute in Japan) and Matthew Kenworth (of Leiden University in the Netherlands) set out to assess how long such a ring system could remain stable for.

For the sake of their study, titled “Constraints on the Size and Dynamics of the J1407b Ring System“, they conducted a series of simulations using the Astrophysical Multi-purpose Software Environment (AMUSE) framework. In the end, their results showed that a ring structure with an 11 year orbital period and a retrograde orbit could survive for at least 10,000 orbits.

In other words, the ring system that they hypothesized back in 2012 could endure for 110,000 years. As Rieder (the lead author on the paper) explained in a statement, the results were surprising, but happened to fit the facts:

“The system is only stable when the rings rotate opposite to how the planet orbits the star. It might be far-fetched: massive rings that rotate in opposite direction, but we now have calculated that a ‘normal’ ring system cannot survive.”

How such a ring system could have come about is a mystery, as retrograde ring systems are quite uncommon. But Rieder and Kenworth have stated that they think it might be the result of a catastrophic event – such as a massive collision – that caused the rings (or the planet) to change the direction of their rotation.

Their results also indicated that a retrograde ring system would allow for eclipses, like the one that was observed in 2007. While there was some chance of these being caused by another object, the results suggested otherwise. “The chance of that is minimal,” said Rieder. “Also, the velocity measured with previous observations may not be right, but that would be very strange, because those measurements are very accurate.”

In the future, Rieder and Kenswoth hope to investigate the mysteries of this ring formation more closely. This will include how it could have formed in the first place, and how it has evolved over time. Their study has been accepted for publication in the journal Astronomy & Astrophysics and be viewed online at arXiv.

Further Reading: astronomie.nl, arXiv

Posted on by David Dickinson

This Weekend: A Hunter’s Full Moon Kicks Off Supermoon Season

The #MemoriesInDNA project intends to create an archive of human knowledge which will be sent to the Moon. Credit and copyright: John Brimacombe.

Ready for some lunar action of proxigean proportions? This weekend’s Full Moon ushers in that most (infamous?) of internet ready cultural memes: that of the Supermoon. This moniker stands above the Blood, Mini, and Full Moons both Black and Blue as the Full Moon of the year that folks can’t seem to get enough of, and astronomers love to hate.

But wait a minute: is this weekend’s Full Moon really the closest of the year?

Nope, though it’s close. But this month’s Full Moon does, however, usher in what we like to call Supermoon season.

Let us explain.

First, we’ll let you in on the Supermoon’s not so secret history. Yes, the meme arose over the last few decades, mostly due to the dastardly deeds of astrologers. Y’know, that well meaning friend/coworker/relative/anonymous person on Twitter that constantly mistakes your passion for the night sky as ‘astrology.’ Anyhow, the idea of the Supermoon has gained new life via the internet, and loosely translates as the closest Full Moon of the year. Sometimes, its dressed up with the slightly science-y sounding ‘a Full Moon along the closest 90% of its orbit’ (!) definition.

Now, to know the orbit of the Moon is to understand celestial mechanics. The Moon’s orbit is indeed elliptical, ranging from an average perigee (its closest point to the Earth) of 362,600 kilometers, to an apogee of 405,400 kilometers distant.

Fun fact: the time it takes the Moon to go from one perigee to the next (27.55 days) is one anomalistic month, a fine pedantic point to bring up to said relative/coworker the next time they refer to you as an astrologer.

And yes, the perigee Full Moon is a thing. We even like to throw about the quixotic term of the proxigean Moon, a time when tidal variations are at an extreme. Plus, all perigees are not created equal, but range from 356,400 kilometers to 370,400 kilometers distant, as the Earth-Moon system not only swings around its common barycenter, but the Sun also drags the entire orbit of the Moon around the Earth, completing one complete revolution every 8.85 years in what’s known as the precession of the line of apsides. Note that the nodes of the Moon’s orbit actually move in the opposite direction, with an 18.6 year period.

The complex motion of the Moon. Image credit: Wikimedia Commons/Geologician/Homunculus2.
The complex motion of the Moon. Image credit: Wikimedia Commons/Geologician/Homunculus2.

Yup, the motion of the Moon has given humanity a fine study in Celestial Mechanics 101. Anyhow, we contend that a more succinct definition for a perigee ‘Supermoon’ is simply a Full Moon that falls within 24 hours of perigee. Under this definition, the Full Moon this Sunday on October 16th occurring at 4:23 Universal Time (UT) certainly meets the criterion, occurring 19 hours and 24 minutes before perigee… as does the Full Moon of November 14th (2.4 hours from perigee) and December 13th (just under 24 hours from perigee).

For extra fun, said November 14th perigee Full Moon is the closest in 30 years; expect Supermoon lunacy to ensue.

A fun place to play with Full and New Moons vs perigee and apogee past present and future is Fourmilab’s Lunar Apogee and Perigee Calculator. Hey, it’s what we do for fun. Looking over these cycles, you’ll notice a pattern of ‘supermoon seasons’ emerge, which moves forward along the calendar about a lunation a year. (that’s our friend the precession of the line of apsides at work again).

(another fun fact: the time it takes for the Moon to return to a similar phase—for example, Full back to Full—is 29.5 days, and known as a synodic month.)

The Full Moon does appear slightly larger at perigee than apogee, to the tune of 29.3′ versus 34.1′ across. This change is enough to notice with the unaided eye, though the Moon is deceptively smaller than it appears: you could, for example, line up 654 ‘Supermoons’ around the local horizon from end to end.

A 'super' vs average Full Moon. Image credit: Marco Langbroek.
A ‘super’ vs average Full Moon. Image credit: Marco Langbroek.

The October Moon is also referred to by the Algonquin Native Americans as the ‘Hunter’s Moon,’ a time to use that extra illumination to track down vital sustenance as the harsh winter approaches. Very occasionally, the Harvest Full Moon falling near the September southward equinox falls in early October (as occurs next year in 2017) and bumps the Hunter’s Moon from its monthly slot.

Be sure to stalk the rising Hunter’s Moon near perigee this weekend. Of course, we’ll be shooting at our prey with nothing more than a camera, as the Full Moon rises from behind the Andalusian foothills.

Posted on by Matt Williams

A New Dwarf Planet Joins The Solar System Family

Based on data obtained by the Dark Energy Survey (DES), a team of scientists have obtained evidence of another TNO beyond Pluto. Credit: ESO/L. Calçada/Nick Risinger

The Kuiper Belt has been an endless source of discoveries over the course of the past decade. Starting with the dwarf planet Eris, which was first observed by a Palomar Observatory survey led by Mike Brown in 2003, many interesting Kuiper Belt Objects (KBOs) have been discovered, some of which are comparable in size to Pluto.

And according to a new report from the IAU Minor Planet Center, yet another body has been discovered beyond the orbit of Pluto. Officially designated as 2014 UZ224, this body is located about 14 billion km (90 AUs, or 8.5 billion miles) from the Sun. This dwarf planet is not only the latest member of the our Solar family, it is also the second-farthest body from our Sun with a stable orbit.

The discovery was made by David Gerdes, a professor of astrophysics at the University of Michigan, and various colleagues associated with at the Dark Energy Survey (DES) – a project which relies on the Cerro Tololo Inter-American Observatory in Chile. In the past, Gerdes’ research has focused on the detection of dark energy and the expansion of the Universe.

The DECam instrument, . Credit: noao.edu
The DECam instrument, shown before it was inserted into the Blanco telescope at the Cerro Tololo Observatory. Credit: noao.edu

Towards this end, DES has spent the past five years surveying roughly one-eighth of the sky using the Dark Energy Camera (DECam), a 570-Megapixel camera mounted on the Victor M. Blanco telescope at Cerro Tololo. This instrument was commissioned by the US. Dept of Energy to conduct surveys of distant galaxies, and Dr. Gerdes had a hand in creating.

Not surprisingly, this same technology has also allowed for discoveries to be made at the edge of the Solar System. Two years ago, this is precisely what Gerdes challenged a group of undergraduate students to do (as part of a summer project). These students examined images taken by DES between 2013-2016 for indications of moving objects. Since that time, the analysis team has grown to include senior scientists, postdocs, graduate and undergraduate students.

Whereas distant stars and galaxies would appear stationary in these images, distant TNOs showed up in different places over time – hence why are called “transients”. As Dr. Gerdes explains in his 2014 UZ224 Fact Sheet, which is available through his University of Michigan homepage:

“To identify transients, we used a technique known as “difference imaging”. When we take a new image, we subtract from it an image of the same area of the sky taken on a different night. Objects that don’t change disappear in this subtraction, and we’re left with only the transients… This process yields millions of transients, but only about 0.1% of them turn out to be distant minor planets. To find them, we must “connect the dots” and determine which transients are actually the same thing in different positions on different nights. There are many dots and MANY more possible ways to connect them.”

Images of 2014 UZ224, shown on three slides obtained by the DECam. Credit: David Gerdes/DES/University of Michigan
Images of 2014 UZ224, shown on three slides obtained by the DECam. Credit: David Gerdes/DES/University of Michigan

This was a difficult process. In addition to needing thousands of computers at Fermilab to process the hundreds of terabytes of data, the team had to write special programs to do it. Gerdes and his colleagues also relied on help from Professors Masao Sako and Gary Bernstein of the University of Pennsylvania, who contributed the key breakthroughs that allowed them to perform difference imaging over the entire survey area.

In the end, dozens of new Trans-Neptunian Objects (TNOs) were discovered, one of which was 2014 UZ224. According to their observations, its diameter could be anywhere from 350 to 1200 km, and it takes 1,136 years to complete a single orbit of our Sun. For the sake of perspective, Pluto is 2370 km in diameter, and has an orbital period of 248 years.

Stephanie Hamilton, a graduate student at the University of Michigan, was personally involved with the project. Her role was to determine the size of 2014 UZ224, which was difficult from initial observations alone. As she told Universe Today via email:

“The object’s brightness in visible light alone depends both on its size and how reflective it is, so you can’t uniquely determine one of those properties without assuming a value for the other. Fortunately there’s a solution to that problem – the heat the object emits is also proportional to its size, so obtaining a thermal measurement in addition to the optical measurements means we would then be able to calculate the object’s size and albedo (reflectance) without having to assume one or the other.

“We were able to obtain an image of our object at a thermal wavelength using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. I am working on combining all of our data together to determine the size and albedo, and we expect to submit a paper on our results around mid-November or so.”

Artistic rendering shows the distant view from theoretical Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)
Artistic rendering shows the distant view from theoretical Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)

But as with all things related to “dwarf planets”, there has been some disagreement over this discovery. Given the dimensions of the object, there are some who question whether or not the label applies. But as Gerdes indicates on the Fact Sheet, this body fits most of the prerequisites:

“According to the official IAU guidelines, a dwarf planet must satisfy four criteria. It must a) orbit the sun (check!), b) not be a satellite (check!) c) not have cleared the neighborhood around its orbit (check!) and d) have enough mass to be round. It’s this last item that’s uncertain, and the only way for sure is to get a picture that’s detailed enough to actually see its shape. Nevertheless, an object over 400 km in diameter is likely to be round.”

Gerdes and his team expect to be busy, authoring the paper that will detail their findings, using the ALMA array to get more assessments of 2014 UZ224 size, and sifting through the data to look for more objects in the Kuiper Belt. This includes the fabled Planet 9, which astronomers have been seeking out for years.

Given its distance from the Sun, 2014 UZ224’s orbit would not be influenced by the presence of Planet 9, and is therefore of no help. However, Gerdes is optimistic that the evidence of this massive body is there in the data. Given time, and a lot of data-processing, they just might find it! In the meantime, this newly discovered object is likely to be the focal point of a lot of fascinating research.

“It’s an interesting object in its own right – distant objects like this are ‘cosmic leftovers’ from the primordial disk that gave birth to the solar system,” writes Gerdes. “By studying them and learning more about their distribution, orbital characteristics, sizes, and surface properties, we can learn more about the processes that gave birth to the solar system and ultimately to us.”

Further Reading: 2014 UZ224 Fact Sheet (University of Michigan)

Posted on by Matt Williams

Turns out Proxima Centauri is Strikingly Similar to our Sun

Artist's depiction of the interior of a low-mass star, such as the one seen in an X-ray image from Chandra in the inset. Credit: NASA/CXC/M.Weiss

In August of 2016, the European Southern Observatory announced that the nearest star to our own – Proxima Centauri – had an exoplanet. Since that time, considerable attention has been focused on this world (Proxima b) in the hopes of determining just how “Earth-like” it really is. Despite all indications of it being terrestrial and similar in mass to Earth, there are some lingering doubts about its ability to support life.

This is largely due to the fact that Proxima b orbits a red dwarf. Typically, these low mass, low temperature, slow fusion stars are not known for being as bright and warm as our Sun. However, a new study produced by researchers at the Harvard Smithsonian Center for Astrophysics (CfA) has indicated that Proxima Centauri might be more like our star than we thought.

For instance, our Sun has what is known as a “Solar Cycle“, an 11-year period in which it experiences changes in the levels of radiation it emits. This cycle is driven by changes in the Sun’s own magnetic field, and corresponds to the appearance of Sunspots on its surface. During a “solar minimum”, the Sun’s surface is clear of spots, while at a solar maximum, one hundred sunspots can appear on an area the size of 1% the Sun’s surface area.

This image is a composite of 25 separate images spanning the period of April 16, 2012, to April 15, 2013. It uses the SDO AIA wavelength of 171 angstroms and reveals the zones on the sun where active regions are most common during this part of the solar cycle. Credit: NASA/SDO/AIA/S. Wiessinger
Composite of 25 separate images spanning the period of April 16, 2012, to April 15, 2013, revealing active regions during this part of the Solar Cycle. Credit: NASA/SDO/AIA/S. Wiessinger

For the sake of their research, the Harvard Smithsonian team examined Proxima Centauri over the course of several years to see if it too had a cycle. As they explain in their research paper, titled “Optical, UV, and X-Ray Evidence for a 7-Year Stellar Cycle in Proxima Centauri” they relied on several years worth optical, UV, and X-ray observations made of the star.

This included 15 years of visual data and 3 years of infrared data from the All Sky Automated Survey (ASAS), 4 years of x-ray and UV data from the Swift x-ray telescope (XRT), and 22 years worth of x-ray observations taken by the Advanced Satellite for Cosmology and Astrophysics (ASCA), the XXM-Newton mission and the Chandra X-ray Observatory.

What they found was that Proxima Centauri does indeed have a cycle that involves changes in its minimum and maximum amount of emitting radiation, which corresponds to “starspots” on its surface. As Dr. Wargelin told Universe Today via email:

“The optical/ASAS data showed a nice 7-year cycle, as well as an 83-day rotation period. When we broke down that data by year we saw the period vary from around 77 to 90 days. We interpret that as ‘differential rotation’ like that found on the Sun. The rotation rate differs at different latitudes; on the Sun it’s around 35 days at the poles and 24.5 at the equator. The “average” rotation is usually given as 27.3 days.”

In essence, Proxima Centauri has its own cycle, but one that is a lot more dramatic than our Sun’s. Besides lasting 7 years from peak to peak, it involves spots covering over 20% of its surface at one time. These spots are apparently much bigger than the ones we regularly observe on our Sun as well.

X-Ray image of Proxima Centauri. Image credit: Chandra
An X-Ray image of Proxima Centauri. Credit: Chandra/Harvard/NASA

This was surprising, given that Proxima’s interior is very different from our Sun’s. Because of its low mass, the interior of Proxima Centauri is convective, where material in the core is transferred outward. In contrast, only the outer layer of our Sun undergoes convection while the core remains relatively still. This means that, unlike our Sun, energy is transferred to the surface through physical movement, and not radiative processes.

While these findings cannot tell us anything directly about whether or not Proxima b might be habitable, the existence of this solar cycle is an interesting find that might be leading in that general direction. As Dr. Wargelin explained:

“Magnetic fields are what drive high energy emission (UV and X rays) and stellar winds (like the solar wind) in solar-type and smaller stars, AND a stellar cycle (if it has one). That X-ray/UV emission and stellar wind can ionize/evaporate/strip the atmosphere of close-in planets, particularly if the planet doesn’t have a protective magnetic field of its own.

“Therefore….. a necessary but not sufficient requirement for understanding (i.e., modeling) the evolution of a planet’s atmosphere is understanding the magnetic field of the host star.  If you don’t understand why a star has a cycle (and standard theory says fully convective stars like Proxima can NOT have cycles) then you don’t understand its magnetic field.”

As always, further observations and research will be necessary before we can fully understand Proxima Centauri, and whether or not any planets that orbit it could support life. But then again, we’ve only known about Proxima b for a short time, and the rate at which we are learning new things about it is quite impressive!

Further Reading: CfA, arXiv

Posted on by Matt Williams

X-Rays Are Coming From The Dark Side of Venus

On June 5th, 2012, the NASA/JAXA Hinode mission captured these stunning views of the transit of Venus. Credit: JAXA/NASA/Lockheed Martin

Venus and Mercury have been observed transiting the Sun many times over the past few centuries. When these planets are seen passing between the Sun and the Earth, opportunities exist for some great viewing, not to mention serious research. And whereas Mercury makes transits with greater frequency (three times since 2000), a transit of Venus is something of a rare treat.

In June of 2012, Venus made its most recent transit – an event which will not happen again until 2117. Luckily, during this latest event, scientists made some very interesting observations which revealed X-ray and ultraviolet emissions coming from the dark side of Venus. This finding could tell us much about Venus’ magnetic environment, and also help in the study of exoplanets as well.

For the sake of their study (titled “X-raying the Dark Side of Venus“) the team of scientists – led by Masoud Afshari of the University of Palermo and the National Institute of Astrophysics (INAF) – examined data obtained by the x-ray telescope aboard the Hinode (Solar-B) mission, which had been used to observe the Sun and Venus during the 2012 transit.

Artist's impression of the Hinode (Solar-B) spacecraft in orbit. Credit: NASA/GSFC/C. Meaney
Artist’s impression of the Hinode (Solar-B) spacecraft in orbit. Credit: NASA/GSFC/C. Meaney

In a previous study, scientists from the University of Palermo used this data to get truly accurate estimates of Venus’ diameter in the X-ray band. What they observed was that in the visible, UV, and soft X-ray bands, Venus’ optical radius (taking into account its atmosphere) was 80 km larger than its solid body radius. But when observing it in the extreme ultraviolet (EUV) and soft X-ray band, the radius increased by another 70 km.

To determine the cause of this, Afshari and his team combined updated information from Hinode’s x-ray telescope with data obtained by the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO). From this, they concluded that the EUV and X-ray emissions were not the result of a fault within the telescope, and were in fact coming from the dark side of Venus itself.

They also compared the data to observations made by the Chandra X-ray Observatory of Venus in 2001 and again in 2006-7m which showed similar emissions coming from the sunlit side of Venus. In all cases, it seemed clear that Venus had unexplained source of non-visible light coming from its atmosphere, a phenomena which could not be chalked up to scattering caused by the instruments themselves.

Comparing all these observations, the team came up with an interesting conclusion. As they state in their study:

“The effect we are observing could be due to scattering or re-emission occurring in the shadow or wake of Venus. One possibility is due to the very long magnetotail of Venus, ablated by the solar wind and known to reach Earth’s orbit… The emission we observe would be the reemitted radiation integrated along the magnetotail.”

On June 5-6 2012, NASA's Solar Dynamics Observatory, or SDO, collected images of one of the rarest predictable solar events: the transit of Venus across the face of the sun. This event happens in pairs eight years apart that are separated from each other by 105 or 121 years. The last transit was in 2004 and the next will not happen until 2117. Credit: NASA/SDO, AIA
Collected images of Venus 2012 transit of the Sun, taken in June of 2012 by NASA’s Solar Dynamics Observatory (SDO). Credit: NASA/SDO, AIA

In other words, they postulate that the radiation observed emanating from Venus could be due to solar radiation interacting with Venus’ magnetic field and being scattered along its tail. This would explain why from various studies, the radiation appeared to be coming from Venus’ itself, thus extending and adding optical thickness to its atmosphere.

If true, this finding would not only help us to learn more about Venus’ magnetic environment and assist our exploration of the planet, it would also improve our understanding of exoplanets. For example, many Jupiter-sized planets have been observed orbiting close to their suns (i.e. “Hot Jupiters“). By studying their tails, astronomers may come to learn much about these planets’ magnetic fields (and whether or not they have one).

Afshari and his colleagues hope to conduct future studies to learn more about this phenomenon. And as more exoplanet-hunting missions (like TESS and the James Webb Telescope) get underway, these newfound observations of Venus will likely be put to good use – determining the magnetic environment of distant planets.

Further Reading: The Astronomical Journal

Posted on by Matt Williams

Is Proxima Centauri b Basically Kevin Costner’s Waterworld?

Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)
Artist's depiction of a waterworld. A new study suggests that Earth is in a minority when it comes to planets, and that most habitable planets may be greater than 90% ocean. Credit: David A. Aguilar (CfA)

The discovery of an exoplanet candidate orbiting around nearby Proxima Centauri has certainly been exciting news. In addition to being the closest exoplanet to our Solar System yet discovered, all indications point to it being terrestrial and located within the stars’ circumstellar habitable zone. However, this announcement contained its share of bad news as well.

For one, the team behind the discovery indicated that given the nature of its orbit around Proxima Centauri, the planet likely in terms of how much water it actually had on its surface. But a recent research study by scientists from the University of Marseilles and the Carl Sagan Institute may contradict this assessment. According to their study, the exoplanet’s mass may consist of up to 50% water – making it an “ocean planet”.

According to the findings of the Pale Red Dot team, Proxima Centauri b orbits its star at an estimated distance of 7 million kilometers (4.35 million mi) – only 5% of the Earth’s distance from the Sun. It also orbits Proxima Centauri with an orbital period of 11 days, and either has a synchronous rotation, or a 3:2 orbital resonance (i.e. three rotations for every two orbits).

Artist’s impression of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Credit: ESO/M. Kornmesser
Artist’s impression of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. Credit: ESO/M. Kornmesser

Because of this, liquid water is likely to be confined to either the sun-facing side of the planet (in the case of a synchronous rotation), or in its tropical zone (in the case of a 3:2 resonance). In addition, the radiation Proxima b receives from its red dwarf star would be significantly higher than what we are used to here on Earth.

However, according to a study led by Bastien Brugger of the Astrophysics Laboratory at the University of Marseilles, Proxima b may be wetter than we previously thought. For the sake of their study, titled “Possible Internal Structures and Compositions of Proxima Centauri b” (which was accepted for publication in The Astrophysical Journal Letters), the research team used internal structure models to compute the radius and mass of Proxima b.

Their models were based on the assumptions that Proxima b is both a terrestrial planet (i.e. composed of rocky material and minerals) and did not have a massive atmosphere. Based on these assumptions, and mass estimates produced by the Pale Red Dot survey (~1.3 Earth masses), they concluded that Proxima b has a radius that is between 0.94 and 1.4 times that of Earth, and a mass that is roughly 1.1 to 1.46 times that of Earth.

As Brugger told Universe Today via email:

“We listed all compositions that Proxima b could have, and ran the model for each of them (that makes about 5000 simulations), giving us each time the corresponding planet radius. We finally excluded all the results that were not compatible with a planetary body, basing on the formation conditions of our solar system (since we do not know these conditions for the Proxima Centauri system). And thus, we obtained a range of possible planet radii for Proxima b, going from 0.94 to 1.40 times the radius of the Earth.”

Goldilocks Zone
Tidally-locked planets like Gliese 581 g (artist’s impression) are likely to be “eyeball” worlds, with a warm-water ocean on the sun-facing side surrounded by ice. Credit: Lynette Cook/NSF

This range in size allows for some very different planetary compositions. At the lower end, being slightly smaller but a bit more massive than Earth, Proxima b would likely be a Mercury-like planet with a 65% core mass fraction. However, at the higher end of the radii and mass estimates, Proxima b would likely be half water by mass.

“If the radius is 0.94 Earth radii, then Proxima b is fully rocky with a huge metallic core (like Mercury in the solar system),” said Brugger. “On the opposite, Proxima b can reach a radius of 1.40 only if it harbors a massive amount of water (50% of the total planet mass), and in this case it would be an ocean planet, with a 200 km deep liquid ocean! Below that, the pressure is so high that the water would turn into ice, forming a ~3000 km thick ice layer (Under which there would be a core made of rocks).”

In other words, Proxima b could be an “eyeball planet”, where the sun-facing side has a liquid ocean surface, while the dark side is covered in frozen ice. Recent studies have suggested that this may be the case with planet’s that orbit within the habitable zones of red dwarf stars, where tidal-locking ensures that only one side gets the heat necessary to maintain liquid water on the surface.

On the other hand, if it has an orbital resonance of 3:2, its likely to have a double-eyeball pattern – with liquid oceans in both the eastern and western hemispheres – while remaining frozen at the terminators and poles. However, if the lower estimates should be true, then Proxima b is likely to be a rocky, dense planet where liquid water is rare on one side, and frozen on the other.

Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO
Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. New research suggest the planet may be more watery than previously thought. Credit: ESO

But perhaps the most interesting aspect of the the research is that it offers a glimpse into the likelihood of Proxima b being habitable. Ever since its discovery, the question of whether or not the planet can support life has remained contentious. But as Brugger explained:

“The interesting part is that all the cases we considered are compatible with a habitable planet. So if the planet radius is finally measured (in some months or years), two cases are possible: either (i) the measurement lies within the 0.94-1.40 range and we will be able to give the exact composition of the planet (and not only a range of possibilities), or (ii) the measured radius is out of this range, and we will know that the planet is not habitable. The case where Proxima b is an ocean planet is particularly interesting, because this kind of planet does not need an atmosphere of oxygen and nitrogen (like on the Earth) to harbor life, since it can develop in its huge ocean.”

But of course, these scenarios are based on the assumption that Proxima b has a lot in common with the planets of our own Solar System. It’s also based on the assumption that the planet is indeed about 1.3 Earth masses. Until the planet can be observed making a transit of Proxima Centauri, astronomers won’t know for sure how massive it is.

Ultimately, we’re still a long ways away from determining Proxima b’s exact size, composition, and surface features – to say nothing about whether or not it can actually support life. Nevertheless, research like this is beneficial in that it helps us to come up with constrains on what kind of planetary conditions could exist there.

And who knows? Someday, we may be able to send probes or crewed missions to the planet, and perhaps they will beam back images of sentient beings navigating vast oceans, looking for some fabled parcel of land they heard about? God I hope not! Once was more than enough!

Further Reading: arXiv

Posted on by Matt Williams

What is Galactic Evolution?

Whirlpool Galaxy M51 (NGC 5194). Credit: Hubble Heritage Team (STScI/AURA) N. Scoville (Caltech)

On a clear night, you can make out the band of the Milky Way in the night sky. For millennia, astronomers looked upon it in awe, slowly coming to the realization that our Sun was merely one of billions of stars in the galaxy. Over time, as our instruments and methods improved, we came to realize that the Milky Way itself was merely one of billions of galaxies that make up the Universe.

Thanks to the discovery of Relativity and the speed of light, we have also come to understand that when we look through space, we are also looking back in time. By seeing an object 1 billion light-years away, we are also seeing how that object looked 1 billion years ago. This “time machine” effect has allowed astronomers to study how galaxies came to be (i.e. galactic evolution).

The process in which galaxies form and evolve is characterized by steady growth over time, which began shortly after the Big Bang. This process, and the eventual fate of galaxies, remain the subject of intense fascination, and is still fraught with its share of mysteries.

Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. The goal of the Frontier Fields is to peer back further than the Hubble Ultra Deep Field and get a wealth of images of galaxies as they existed in the first several hundred million years after the Big Bang. Note that the unit of time is not linear in this illustration. Illustration Credit: NASA and A. Feild (STScI)
Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)

Galaxy Formation:

The current scientific consensus is that all matter in the Universe was created roughly 13.8 billion years ago during an event known as the Big Bang. At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity. Suddenly, the Singularity began expanding, and the Universe as we know it began.

After rapidly expanding and cooling, all matter was almost uniform in distribution. Over the course of the several billion years that followed, the slightly denser regions of the Universe began to become gravitationally attracted to each other. They therefore grew even denser, forming gas clouds and large clumps of matter.

These clumps became primordial galaxies, as the clouds of hydrogen gas within the proto-galaxies underwent gravitational collapse to become the first stars. Some of these early objects were small, and became tiny dwarf galaxies, while others were much larger and became the familiar spiral shapes, like our own Milky Way.

Galactic Mergers:

Once formed, these galaxies evolved together in larger galactic structures called groups, clusters and superclusters. Over time, galaxies were attracted to one another by the force of their gravity, and collided together in a series of mergers. The outcome of these mergers depends on the mass of the galaxies in the collision.

Small galaxies are torn apart by larger galaxies and added to the mass of larger galaxies. Our own Milky Way recently devoured a few dwarf galaxies, turning them into streams of stars that orbit the galactic core. But when large galaxies of similar size come together, they become giant elliptical galaxies.

When this happens, the delicate spiral structure is lost, and the merged galaxies become large and elliptical. Elliptical galaxies are some of the largest galaxies ever observed. Another consequence of these mergers is that the supermassive black holes (SMBH) at their centers become even larger.

Not all mergers will result in elliptical galaxies, mind you. But all mergers result in a change in the structure of the merged galaxies. For example, it is believed that the Milky Way is experiencing a minor merger event with the nearby Magellanic Clouds; and in recent years, it has been determined that the Canis Major dwarf galaxy has merged with our own.

While mergers are seen as violent events, actual collisions are not expected to happen between star systems, given the vast distances between stars. However, mergers can result in gravitational shock waves, which are capable of triggering the formation of new stars. This is what is predicted to happen when our own Milky Way galaxy merges with the Andromeda galaxy in about 4 billion years time.

Galactic Death:

Ultimately, galaxies cease forming stars once they deplete their supply of cold gas and dust. As the supply runs out, star forming slows over the course of billions of years until it ceases entirely. However, ongoing mergers will ensure that fresh stars, gas and dust are deposited in older galaxies, thus prolonging their lives.

At present, it is believed that our galaxy has used up most of its hydrogen, and star formation will slow down until the supply is depleted. Stars like our Sun can only last for 10 billion years or so; but the smallest, coolest red dwarfs can last for a few trillion years. However, thanks to the presence of dwarf galaxies and our impending merger with Andromeda, our galaxy could exist even longer.

However, all galaxies in this vicinity of the Universe will eventually become gravitationally bound to each other and merge into a giant elliptical galaxy. Astronomers have seen examples of these sorts of “fossil galaxies”, a good of which is Messier 49 – a supermassive elliptical galaxy.

These galaxies have used up all their reserves of star forming gas, and all that’s left are the longer lasting stars. Eventually, over vast lengths of time, those stars will wink out one after the other, until the whole thing is the background temperature of the Universe.

After our galaxy merges with Andromeda, and goes on to merge with all other nearby galaxies in the local group, we can expect that it too will undergo a similar fate. And so, galaxy evolution has been occurring over billions of years, and it will continue to happen for the foreseeable future.

We have written many articles about galaxies for Universe Today. Here’s What is the Milky Way?, How did the Milky Way Form?, What Happens When Galaxies Collide?, What Happens When Galaxies Die?, A New Spin on Galactic Evolution, and Supercomputer will Study Galaxy Evolution,

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.

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