Universe Today

October 19, 2010November 7, 2016 by Jon Voisey

Stolen: Magellanic Clouds – Return to Andromeda

The Magellanic Clouds are an oddity. Their relative velocity is suspiciously close to the escape velocity of the Milky Way system making it somewhat difficult for them to have been formed as part of the system. Additionally, their direction of motion is nearly perpendicular to the disk of the galaxy and systems, especially ones as large as the Magellanic Clouds, should show more orientation to the plane if they formed along side. Their gas content is also notably different than other satellite galaxies of our galaxy. The combination of these features suggests to some, that the Magellanic Clouds aren’t native to the Milky Way and were instead intercepted.

But where did they come from? Although the suggestion is not entirely new, a recent paper, accepted to the Astrophysical Journal Letters, suggests they may have been captured after a past merger in the Andromeda Galaxy (M31).

To analyze this proposition, the researchers, Yang (from the Chinese Academy of Sciences) and Hammers (of the University of Paris, Diderot), conducted simulations backtracking the positions of the Magellanic Clouds. While this may sound straightforward, the process is anything but. Since galaxies are extended objects, their three dimensional shapes and mass profiles must be worked out extremely well to truly account for the path of motion. Additionally, the Andromeda galaxy is certainly moving and would have been in a different position that it is observed today. But exactly where was it when the Magellanic Clouds would have been expelled? This is an important question, but not easy to answer given that observing the proper motions of objects so far away is difficult.

But wait. There’s more! As always, there’s a significant amount of the mass that can’t be seen at all! The presence and distribution of dark matter would greatly have affected the trajectory of the expelled galaxies. Fortunately, our own galaxy seems to be in a fairly quiescent phase and other studies have suggested that dark matter halos would be mostly spherical unless perturbed. Furthermore, distant galaxy clusters such as the Virgo supercluster as well as the “Great Attractor” would have also played into the trajectories.

These uncertainties take what would be a fairly simple problem and turn it into a case in which the researchers were instead forced to explore the parameter space with a range of reasonable inputs to see which values worked. In doing so, the pair of astronomers concluded “it could be the case, within a reasonable range of parameters for both the Milky Way and M31.” If so, the clouds spent 4 – 8 billion years flying across intergalactic space before being caught by our own galaxy.

But could there be further evidence to support this? The authors note that if Andromeda underwent a merger event of such scale would likely have induced vast amounts of star formation. As such, we should expect to see an increase in numbers of stars with this age. The authors do not make any statements as to whether or not this is the case. Regardless, the hypothesis is interesting and reminds us how dynamic our universe can be.

October 19, 2010April 26, 2016 by Nancy Atkinson

Underground Acquifers Fed Long-Lived Oceans, Lakes on Ancient Mars

Artist's impression of water under the Martian surface. If underground aquifers really do exist, the implications for human exploration and eventual colonization of the red planet would be far-reaching. (Illustration: ESA)

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Images from the spacecraft orbiting Mars seem to indicate the Red Planet may once have had oceans and lakes, and researchers are still trying to figure out how these bodies of water could have developed. A new explanation is that underground aquifers fed water to the surface, forming the floors of ancient continental-scale basins on Mars. The groundwater emerged through extensive and widespread fractures, leading to the formation of river systems, large-scale regional erosion, sedimentary deposition and water ponding in widespread and long-lasting bodies of water in Mars northern plains.

J. Alexis Palmero Rodriguez, research scientist at the Planetary Science Institute PSI, has been studying the Martian northern lowlands region, finding extensive sedimentary deposits that resemble the abyssal plains of Earth’s ocean floors. It is also like the floors of other basins on Mars where oceans are thought to have developed.

The origin of these deposits and the formation of Martian lakes and seas has been a controversial subject over the years. One theory is that there was a sudden release of large volumes of water and sediment from zones of apparent crustal collapse known as “chaotic terrains.” However, these zones of collapse are on the whole rare on Mars, while the plains deposits are widespread and common within large basin settings, Rodriguez said.

From evidence in the planet’s northern plains (south of Gemini Scopuli in Planum Boreum), Rodriguez’ new model does not require sudden massive groundwater discharges. Instead, it advocates for groundwater discharges being widespread, long-lived and common in the northern plains of Mars.

Large gully on Mars, seen by the Mars Reconnaissance Orbiter's HiRISE camera. Credit: NASA/JPL/University of Arizona

“With the loss over time of water from the subsurface aquifer, areas of the northern plains ultimately collapsed, creating the rough hilly surfaces we see today. Some plateaus may have avoided this fate and preserved sedimentary plains containing an immense record of hydrologic activity,” Rodriguez said. “The geologic record in the collapsed hilly regions would have been jumbled and largely lost.

“This model implies that groundwater discharges within basin settings on Mars may have been frequent and led to formation of mud pools, lakes and oceans. In addition, our model indicates this could have happened at any point in the planet’s history,” he said. “There could have been many oceans on Mars over time.”

If life existed in Martian underground systems, life forms could have been brought up to the surface via the discharges of these deep-seated fluids. Organisms and their fossils may therefore be preserved within some of these sedimentary strata, Rodriguez said.

His paper was published in the journal Icarus.

Source: Planetary Science Institute

October 19, 2010December 24, 2015 by Nancy Atkinson

365 Days of Astronomy Podcast to Continue in 2011

If you’ve been considering contributing a podcast to the 365 Days of Astronomy but just haven’t gotten around to it yet, there’s good news: the project will be continuing for another year — its third — in 2011. As far as we can tell, 365 Days of Astronomy is the most popular and successful user-generated podcast ever, as each podcast is listened to thousands of times. If you’re looking to share your experiences, thoughts, feelings, discoveries, or anything about space and astronomy, this is your big chance to find your voice and an audience to listen.

Since it is now the Year of the Solar System, it seemed like a good reason to keep this Energizer-Bunny project from the International Year of Astronomy going for another year. As the Project Manager, I hope you’ll join in, or at least check it out and start listening daily — if you aren’t already. Here’s the official press release:

The award-winning 365 Days of Astronomy Podcast is proud to announce the project will continue for yet another year – its third year — and is now accepting sign-ups for participants for another 365 podcasts in 2011. 2011 encompasses the Year of the Solar System, which marks an unprecedented flurry of robotic exploration of space, and is the perfect opportunity for more of the public to become involved in creating podcasts to share astronomy with the world.

365 Days of Astronomy is a legacy project of the International Year of Astronomy (IYA), and in 2009 was a major project of the IYA. For two years now, the project has published one podcast for every day of the year. The episodes are written, recorded and produced by people all around the world. “This podcast gives a voice to everyone in astronomy – professionals, amateurs, and those who just enjoy the amazing discoveries and images of our Universe,” said Dr. Pamela Gay, chair for the IYA’s New Media Group.

The 365 Days of Astronomy podcast is now looking for individuals, schools, companies and clubs to submit 5 – 10 minutes of audio for our daily podcast.

The 365 Days of Astronomy has gained a wide audience, and each podcast is heard by 5,000 – 10,000 listeners. The project was awarded a Parsec Award in 2009 for “The Best Info-tainment” podcast in 2009, and was nominated for the “Best Fact Behind the Fiction” award in 2010.

Participants can sign up to do just 1 episode or up to 12 episodes (one per month, subject to editorial discretion). People from every continent except Antarctica have submitted podcasts the past two years, and the 365 Days of Astronomy team encourages a more diverse population from even more countries to sign up for a particular day (or days) of 2011. A calendar of astronomical events is available on the project’s website to provide ideas but the podcasts can be about virtually any astronomical topic. “We are seeking a wide range of contributions, from simple concepts or how-tos to more in-depth discussions of complex concepts,” said Dr. Gay. “Over the past two years, we received a wide range of contributions, from simple at-home first-time podcasts to highly polished and professional recordings. We expect the same for 2011 and are looking to sign up a variety of participants, from amateur astronomers, classroom teachers and students to scientists, science bloggers and big media companies.”

The project is also asking individuals and organizations for financial support.

The podcast team also invites people and organizations to sponsor the podcast by donating $30 to support 1 day of the podcast, with your dedication appearing at the start of the show. For just $360, it is possible to sponsor 1 episode per month. Alternatively, you can also have a dedication message at the end of the show for a week, for a donation at the $100 level. These donations will help pay for editing, and posting of the podcasts.

For more information visit:

365 Days of Astronomy: http://365DaysOfAstronomy.org.

Astrosphere New Media: http://www.astrosphere.org/

Year of the Solar System: http://solarsystem.nasa.gov/yss/index.cfm

October 19, 2010December 24, 2015 by Jon Voisey

The Habitability of Gliese 581d

The Gliese 581 system has been making headlines recently for the most newly announced planet that may lie in the habitable zone. Hopes were somewhat dashed when we were reminded that the certainty level of its discovery was only 3 sigma (95%, whereas most astronomical discoveries are at or above the 99% confidence level before major announcements), but the Gliese 581 system may yet have more surprises. When the second planet, Gliese 581d, was first discovered, it was placed outside of the expected habitable zone. But in 2009, reanalysis of the data refined the orbital parameters and moved the planet in, just to the edge of the habitable zone. Several authors have suggested that, with sufficient greenhouse gasses, this may push Gliese 581d into the habitable zone. A new paper to be published in an upcoming issue of Astronomy & Astrophysics simulates a wide range of conditions to explore just what characteristics would be required.

The team, led by Robin Wordsworth at the University of Paris, varied properties of the planet including surface gravity, albedo, and the composition of potential atmospheres. Additionally, the simulations were also run for a planet in a similar orbit around the sun (Gliese 581 is an M dwarf) to understand how the different distribution of energy could effect the atmosphere. The team discovered that, for atmospheres comprised primarily of CO₂, the redder stars would warm the planet more than a solar type star due to the CO₂ not being able to scatter the redder light as well, thus allowing more to reach the ground.

One of the potential roadblocks to warming the team considered was the formation of clouds. The team first considered CO₂ clouds which would be likely towards the outer edges of the habitable zone and form on Mars. Since clouds tend to be reflective, they would counteract warming effects from incoming starlight and cool the planet. Again, due to the nature of the star, the redder light would mitigate this somewhat allowing more to penetrate a potential cloud deck.

Should some H₂O be present its effects are mixed. While clouds and ice are both very reflective, which would decrease the amount of energy captured by a planet, water also absorbs well in the infrared region. As such, clouds of water vapor can trap heat radiating from the surface back into space, trapping it and resulting in an overall increase. The problem is getting clouds to form in the first place.

The inclusion of nitrogen gas (common in the atmospheres of planets in the solar system) had little effect on the simulations. The primary reason was the lack of absorption of redder light. In general, the inclusion only slightly changed the specific heat of the atmosphere and a broadening of the absorption lines of other gasses, allowing for a very minor ability to trap more heat. Given the team was looking for conservative estimates, they ultimately discounted nitrogen from their final considerations.

With the combination of all these considerations, the team found that even given the most unfavorable conditions of most variables, should the atmospheric pressure be sufficiently high, this would allow for the presence of liquid water on the surface of the planet, a key requirement for what scientists maintain is critical for abiogenesis. The favorable merging of characteristics other than pressure were also able to produce liquid water with pressures as low as 5 bars. The team also notes that other greenhouse gasses, such as methane, were excluded due to their rarity, but should the exist, the ability for liquid water would be improved further.

Ultimately, the simulation was only done as a one dimensional model which essentially considered a thin column of the atmosphere on the day side of the planet. The team suggests that, for a better understanding, three dimensional models would need to be created. In the future, they plan to use just such modeling which would allow for a better understanding of what was happening elsewhere on the planet. For example, should temperatures fall too quickly on the night side, this could lead to the condensation of the gasses necessary and put the atmosphere in an unstable state. Additionally, as we discover more transiting exoplanets and determine their atmospheric properties from transmission spectra, astronomers will better be able to constrain what typical atmospheres really look like.

October 19, 2010December 24, 2015 by Nancy Atkinson

Hubble Spins the Wheel on Star Birth

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Galaxies are like snowflakes, with no two looking exactly the same. The latest image released from the Hubble Space Telescope shows a striking face-on spiral galaxy named NGC 3982, which is a swirl of activity and star birth along with its winding arms. The arms are lined with pink star-forming regions of glowing hydrogen, newborn blue star clusters, and obscuring dust lanes that provide the raw material for future generations of stars. The bright nucleus is home to an older population of stars, which grow ever more densely packed toward the center.

NGC 3982 is located about 68 million light-years away in the constellation Ursa Major. The galaxy spans about 30,000 light-years, one-third of the size of our Milky Way galaxy. This color image is composed of exposures taken by three different instruments, taken over a substantial portion of the space telescope’s life, from March 2000 and August 2009: The Wide Field Planetary Camera 2 (WFPC2), the Advanced Camera for Surveys (ACS), and the Wide Field Camera 3 (WFC3). The observations were taken between The rich color range comes from the fact that the galaxy was photographed in visible and near-infrared light. Also used was a filter that isolates hydrogen emission that emanates from bright star-forming regions dotting the spiral arms.

Source: HubbleSite

October 18, 2010October 18, 2010 by Nancy Atkinson

First Rickroll in Space

Those pranksters from Zug have now gone to the edge of space, sending their own DIY satellite up to 89,000 feet above Earth, and doing a little Rickrolling along the way. They claim they have now pulled the famous prank on the entire planet. Hmmm, hopefully this wasn’t the source of the radio signals that caused ESA’s Soil Moisture and Ocean Salinity (SMOS) probe to be “blinded from interference.” Surely strains of “Never Gonna Give You Up” could never do that….

The video above is a quick look at their balloon satellite launch and their results; here’s the whole story on Zug.

October 17, 2010April 26, 2016 by Matt Williams

Destructive Interference

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Sound travels in waves, which function much the same as ocean waves do. One wave cycle is a complete wave, consisting of both the up half (crest) and down half (trough). Waves also have a certain amplitude which is the measure of how strong the wave is; the higher the amplitude, the higher the crests and deeper the troughs. Waves don’t usually reflect when they strike other waves. Instead, they combine. If the amplitudes of two waves have the same sign (either both positive or both negative), they will add together to form a wave with a larger amplitude. This is called constructive interference. If the two amplitudes have opposite signs, they will subtract to form a combined wave with lower amplitude. This is what is called Destructive Interference, which is a subfield of the larger study in physics known as wave propagation.

An interesting example of this is the loudspeaker. When music is played on the loudspeaker, sound waves emanate from the front and back of the speaker. Since they are out of phase, they diffract into the entire region around the speaker. The two waves interfere destructively and cancel each other, particularly at very low frequencies. But when the speaker is held up behind baffle, which in this case consists of a wooden sheet with a circular hole cut in it, the sounds can no longer diffract and mix while they are out of phase, and as a consequence the intensity increases enormously. This is why loudspeakers are often mounted in boxes, so that the sound from the back cannot interfere with the sound from the front.

Scientists and engineers use destructive interference for a number of applications to levels reduce of ambient sound and noise. One example of this is the modern electronic automobile muffler. This device senses the sound propagating down the exhaust pipe and creates a matching sound with opposite phase. These two sounds interfere destructively, muffling the noise of the engine. Another example is in industrial noise control. This involves sensing the ambient sound in a workplace, electronically reproducing a sound with the opposite phase, and then introducing that sound into the environment so that it interferes destructively with the ambient sound to reduce the overall sound level.

For a hands-on demonstration of how destructive interference works, click on this link.

We have written many articles about destructive interference for Universe Today. Here’s an article about constructive waves, and here’s an article about the Casimir Effect.

If you’d like more info on destructive interference, check out Running Interference, and here’s a link to NASA Science page about Interference.

We’ve also recorded an entire episode of Astronomy Cast all about the Wave Particle Duality. Listen here, Episode 83: Wave Particle Duality.

Sources:
http://en.wikipedia.org/wiki/Interference_%28wave_propagation%29
http://en.wikipedia.org/wiki/Loudspeaker_enclosure
http://en.wikipedia.org/wiki/Sound_baffle
http://www.windows2universe.org/earth/Atmosphere/tornado/beat.html
http://library.thinkquest.org/19537/Physics5.html
http://zonalandeducation.com/mstm/physics/waves/interference/destructiveInterference/InterferenceExplanation3.html

October 17, 2010April 26, 2016 by Matt Williams

Desertification

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The Sahelian-drought, that began in 1968 and took place in sub-Saharan Africa, was responsible for the deaths of between 100,000 to 250,000 people, the displacement of millions more and the collapse of the agricultural base for several African nations. In North America during the 1930’s, parts of the Canadian Prairies and the “Great Planes” in the US turned to dust as a result of drought and poor farming practices. This “Dust Bowl” forced countless farmers to abandon their farms and way of life and made a fragile economic situation even worse. In both cases, a combination of factors led to the process known as Desertification. This is defined as the persistent degradation of dryland ecosystems due to natural and man-made factors, and it is a complex process.

Desertification can be caused by climactic variances, but the chief cause is human activity. It is principally caused by overgrazing, overdrafting of groundwater and diversion of water from rivers for human consumption and industrial use. Add to that overcultivation of land which exhausts the soil and deforestation which removes trees that anchor the soil to the land, and you have a very serious problem! Today, desertification is devouring more than 20,000 square miles of land worldwide every year. In North America, 74% of the land in North America is affected by desertification while in the Mediterranean, water shortages and poor harvests during the droughts of the early 1990s exposed the acute vulnerability of the Mediterranean region to climatic extremes.

In Africa, this presents a serious problem where more than 2.4 million acres of land, which constitutes 73% of its drylands, are affected by desertification. Increased population and livestock pressure on marginal lands have accelerated this problem. In some areas, where nomads still roam, forced migration causes these people to move to new areas and place stress on new lands which are less arid and hence more vulnerable to overgrazing and drought. Given the existing problems of overpopulation, starvation, and the fact that imports are not a readily available option, this phenomenon is likely to lead to greater waves of starvation and displacement in the near future.

Against this backdrop, the prospect of a major climate change brought about by human activities is a source of growing concern. Increased global mean temperatures will mean more droughts, higher rates of erosion, and a diminished supply land water; which will seriously undermine efforts to combat drought and keep the world’s deserts from spreading further. The effects will be felt all over the world but will hit the equatorial regions of the world especially hard, regions like Sub-Saharan Africa, the Mediterranean, Central and South America, where food shortages are already a problem and are having serious social, economic and political consequences.

We have written many articles about desertification for Universe Today. Here’s an article about the largest desert on Earth, and here’s an article about the Atacama Desert.

If you’d like more info on desertification, check out Visible Earth Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:
http://en.wikipedia.org/wiki/Desertification
http://www.greenfacts.org/en/desertification/index.htm
http://archive.greenpeace.org/climate/science/reports/desertification.html
http://pubs.usgs.gov/gip/deserts/desertification/
http://didyouknow.org/deserts/
http://en.wikipedia.org/wiki/Overdrafting

October 16, 2010December 24, 2015 by Steve Nerlich

Astronomy Without A Telescope – No Metal, No Planet

The spiral galaxy NGC 4565, considered a close analogue of the Milky Way and with distinctly dusty outer regions. Credit: ESO.

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A Japanese team of astronomers have reported a strong correlation between the metallicity of dusty protoplanetary disks and their longevity. From this finding they propose that low metallicity stars are much less likely to have planets, including gas giants, due to the shorter lifetime of their protoplanetary disks.

As you are probably aware, ‘metal’ is astronomy-speak for anything higher up the periodic table than hydrogen and helium. The Milky Way has a metallicity gradient – where metallicity drops markedly the further out you go. In the extreme outer galaxy, about 18 kiloparsecs out from the centre, the metallicity of stars is only 10% that of the Sun (which is about 8 kiloparsecs – or around 25,000 light years – out from the centre).

This study compared young star clusters within stellar nurseries with relatively high metallicity (like the Orion nebula) against more distant clusters in the outer galaxy within low metallicity nurseries (like Digel Cloud 2).

The study’s conclusions are based on the assumption that the radiation output of stars with dense protoplanetary disks will have an excess of near and mid-infra red wavelengths. This is largely because the star heats its surrounding protoplanetary disk, making the disk radiate in infra-red.

The research team used the 8.2 metre Subaru Telescope and a procedure called JHK photometry to identify a measure they called ‘disk fraction’, representing the density of the protoplanetary disk (as determined by the excess of infra red radiation). They also used another established mass-luminosity relation measure to determine the age of the clusters.

Graphing disk fraction over age for populations of Sun-equivalent metallicity stars versus populations of low metallicity stars in the outer galaxy suggests that the protoplanetary disks of those low metallicity stars disperse much quicker.

Left image - The Subaru Telescope in Hawaii. Credit: NAOJ. Right image - the relationship between disk persistence for low metallicity stars (O/H = -0.7, red line) and stars with Sun-equivalent metallicity (O/H = 0, black line). The protoplanetary disks of low metal stars seem to disperse quickly, reducing the likelihood of planet formation. Credit: Yasui et al.

The authors suggest that the process of photoevaporation may underlie the shorter lifespan of low metal disks – where the impact of photons is sufficient to quickly disperse low atomic mass hydrogen and helium, while the presence of higher atomic weight metals may deflect those photons and hence sustain a protoplanetary disk over a longer period.

As the authors point out, the lower lifetime of low metallicity disks reduces the likelihood of planet formation. Although the authors steer clear of much more speculation, the implications of this relationship seem to be that, as well as expecting to find less planets around stars towards the outer edge of the galaxy – we might also expect to find less planets around any old Population II stars that would have also formed in environments of low metallicity.

Indeed, these findings suggest that planets, even gas giants, may have been exceedingly rare in the early universe – and have only become commonplace later in the universe’s evolution – after stellar nucleosynthesis processes had adequately seeded the cosmos with metals.

Further reading: Yasui, C., Kobayashi, N., Tokunaga, A., Saito, M. and Tokoku, C.
Short Lifetime of Protoplanetary Disks in Low-Metallicity Environments

October 15, 2010December 19, 2016 by Tega Jessa

Why is the Earth Tilted?

Winter Solstice — Earth as viewed from the cabin of the Apollo 11 spacecraft. Credit: NASA

Have you ever wondered why the Earth is tilted instead of just perpendicular with its plane of orbit? Scientists have taken a crack at answering that question. The main consensus is that it has to do with Earth’s formation along with the rest of the planets in the Solar system. This time in cosmic history is still a mystery to us but we do have some ideas about what went on. We know that the birth of the Sun created a new source of gravity in the young Solar System. The tidal forces between the young sun and the rest of the nebula the Sun was born from created further instability in the gases and dust left in the nebula. This allowed for the steady formation of the planets.

After millions of years passed enough matter collided to gain mass and its own gravity and become small versions of planets called planetessimals and protoplanets. These pre-planets collided to create even larger planets. This set the stage for how the Earth approached its final form. It looks like it probably collided with a another proto-planet and in the process it was tilted.

All the same the Earth’s tilt is very important. It is perfectly positioned so that it gives us the seasons and on top of that the seasons are near perfectly calibrated for life. When compared with other planets Earth’s tilt allows for season that are not too extreme in temperature but are pretty well balanced. At the same if it had stay in the “perfect” position one side of the Earth would be too hot at time and then too cold.

We have written many articles about the Earth’s tilt for Universe Today. Here’s an article about why Earth has seasons, and here’s an article about the Earth’s axis.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.