A "super star cluster", Westerlund 1, which is about 16,000 light-years from Earth. It can be found in the southern constellation of Ara. The picture was taken from the European Southern Observatory's VLT Survey Telescope. Credit: ESO/VPHAS+ Survey/N. Wright
The faint green glow you see in that picture is not an early harbringer of Hallowe’en spooks. It’s hydrogen gas clouds found recently nearby W26, a future supernova in the star cluster Westerlund 1.
The European Southern Observatory’s VLT Survey Telescope in Chile spotted the hydrogen in the cluster, which has hundreds of huge stars that are only believed to be a few million years old. (Our solar system, by comparison, is about 4.5 billion years old.)
“Such glowing clouds around massive stars are very rare, and are even rarer around a red supergiant— this is the first ionised nebula discovered around such a star,” the European Southern Observatory stated.
“W26 itself would be too cool to make the gas glow; the astronomers speculate that the source of the ionizing radiation may be either hot blue stars elsewhere in the cluster, or possibly a fainter, but much hotter, companion star to W26.”
Funny enough, the nebula that surrounds the red supergiant is similar to the one surrounding SN1987A, a star that exploded as a fairly bright supernova in 1987. “Studying objects like this new nebula around W26 will help astronomers to understand the mass loss processes around these massive stars, which eventually lead to their explosive demise,” ESO added.
And if you’re interested in looking back, here’s an archive to all the past Carnivals of Space. If you’ve got a space-related blog, you should really join the carnival. Just email an entry to [email protected], and the next host will link to it. It will help get awareness out there about your writing, help you meet others in the space community – and community is what blogging is all about. And if you really want to help out, sign up to be a host. Send an email to the above address.
You can always count on an eclipse to get you out of a delicate situation. Today is Columbus Day in the United States and Thanksgiving north of the border in Canada. Later this week also marks the start of the second eclipse season for 2013. Today, we thought we’d take a look at the circumstances for the first eclipse of the season kicking off this coming Friday night, October 18, as well as the fascinating role that eclipses played in the life and times of Christopher Columbus.
Friday’s event is a penumbral lunar eclipse, meaning that the Full Moon will only pass through the outer bright rim of the Earth’s shadow. Such events are subtle affairs, as opposed to total and partial lunar eclipses, which occur when the Moon enters the dark inner core, or umbra, of the Earth’s shadow. Still, you may just be able to notice a slight dusky shading on the lower southern limb of the Moon as it flirts with the umbra, barely missing it around the time of central eclipse at 23:51 Universal Time/ 7:51 PM Eastern Daylight Saving Time. Friday night’s penumbral is 3 hours and 59 minutes in duration, and 76.5% of the disk of the Moon will be immersed in the penumbra at maximum eclipse.
The visibility footprint and circumstances of this week’s penumbral lunar eclipse. (Credit: Fred Espenak/NASA/GSFC).
Key Events occurring on Friday, October 18th:
21:50UT/5:50PM EDT: 1st contact with the Earth’s shadow.
23:51UT/7:51PM EDT: Mid-eclipse.
01:49UT(Oct 19th)/9:49PM EDT: Last contact. Eclipse ends.
The eclipse will be underway at moonrise for North and South America and occur at moonset for central Asia— Africa and Europe will see the entire eclipse. Standing on Earth’s Moon, an observer on the nearside would see a partial solar eclipse.
A simulation of Friday’s lunar eclipse, looking back from Moon at mid-eclipse. (Wikimedia Commons graphic in the Public Domain).
This eclipse is the 3rd and final lunar eclipse of 2013, and the 5th overall. It’s also the first in a series of four descending node eclipses, including the total lunar eclipse of October 8th next year. It’s also the 52nd eclipse of 72 in the lunar saros series 117, which started on April 3rd, 1094 and will end with a final lunar eclipse on May 15th, 2356. Saros 117 produced its last total lunar eclipse in 1815 and its final partial in 1941.
Though penumbrals are slight events, we’ve been able to notice an appreciable difference before, during and after the eclipse photographically:
Can you spy the difference? The May 18th, 2002 penumbral lunar eclipse before (left) and during mid-eclipse (right). Photos by Author.
Be sure to use identical exposure settings to catch this effect. Locations where the Moon rides high in the sky also stand the best chance of imaging the faint penumbral shading, as the Moon will be above the discoloring effects of the thicker air mass low to the horizon.
The Moon reaches descending node along the ecliptic about 20 hours after the end of the eclipse, and reaches apogee just over six days later on October 25th. The October Full Moon is also known as the Hunter’s Moon, providing a bit of extra illumination on the Fall hunt.
And this sets us up for the second eclipse of the season the next time the Moon crosses an ecliptic node, a hybrid (annular-total) solar eclipse spanning the Atlantic and Africa on November 3rd. More to come on that big ticket event soon!
In Columbus’s day, the Moon was often used to get a rough fix of a ship’s longitude at sea. Columbus was especially intrigued with the idea of using lunar eclipses to determine longitude. If you can note the position of the Moon in the sky from one location versus a known longitude during an event— such as first contact of the Moon with the Earth’s umbra during an eclipse —you can gauge your relative longitude east or west of the point. The sky moves 15 degrees, or one hour of right ascension overhead as we rotate under it. One of the earliest records of this method comes to us from Ptolemy, who deduced Alexander the Great’s position 30 degrees (2 hours) east of Carthage during the lunar eclipse of September 20th, 331 B.C. Alexander noted that the eclipse began two hours after sunset from his locale, while in Carthage it was recorded that the eclipse began at sunset.
A Jacob’s cross staff, a simple tool for measuring angles in the sky. (Charles Towne Landing Historic Site Museum, Photo by Author).
Columbus was a student of Ptolemy, and used this method during voyages to and from the New World during the lunar eclipses of September 14th, 1494 and February 29, 1504. Of course, such a method is only approximate. The umbra of the Earth often appears ragged and indistinct on the edge of the lunar disk at the start of an eclipse, making it tough to judge the actual beginning of an eclipse by more than ten of minutes or so. And remember, you’re often watching from the pitching deck of a ship to boot!
Another problem also plagued Columbus’s navigation efforts: he favored a smaller Earth than we now know is reality. Had he listened to another Greek astronomer by the name of Eratosthenes, he would’ve gotten his measurements pretty darned close.
An eclipse also saved Columbus’s butt on one occasion. The story goes that tensions had come to a head between the locals and Columbus’s crew while stranded on the island of Jamaica in 1504. Noting that a lunar eclipse was about to occur on March 1st (the evening of February 29th for North America), Columbus told the local leader that the Moon would rise “inflamed with wrath,” as indeed it did that night, right on schedule. Columbus then made a great show of pretending to pray for heavenly intersession, after which the Moon returned to its rightful color. This kept a conniving Columbus and his crew stocked in supplies until a rescue ship arrived in June of that year.
A depiction of the 1504 lunar eclipse from the 1879 text Astronomie Populare by Camille Flammarion.
Be sure to check out this Friday’s penumbral eclipse, and amaze your friends with the prediction of the next total lunar eclipse which occurs on U.S. Tax Day next year on April 15th, 2014. Can you do a better job of predicting your longitude than Columbus?
Frame grab from a video of the Feb. 15, 2013 Russian fireball by Aleksandr Ivanov
The meteor explosion over Russia in February 2013 raised concerns that even small asteroid impactors may wreak some havoc given our heavily populated cities. A new study by NASA scientists aims to improve our understanding of such asteroids that are lurking in Earth’s vicinity. The team, led by Amy Mainzer, noted that only a mere fraction of asteroids comparable in size to the object that exploded over Russia have been discovered, and their physical properties are poorly characterized.
The team derived fundamental properties for over a hundred near-Earth objects, and determined that many are smaller than 100 meters. Indeed, the team notes that, “In general … [asteroids] smaller than 100-m are only detected when they are quite close … and the smallest … were detected when they were only 2-3 lunar distances away from Earth.”
Essentially, a large fraction of these bodies may go undetected until they strike Earth, analogous to the case of the asteroid that exploded over Russia in February.
The team’s results rely partly on observations from the Wide-field Infrared Survey Explorer (WISE), which is a space-based telescope that mapped the entire sky in the mid-infrared. Observations taken in the infrared, in concert with those taken in the optical, can be used to infer the fundamental properties of asteroids (e.g., their diameter and chemical composition).
On a somewhat positive note, Mainzer remarks that 90% of near-Earth asteroids larger than 1-km are known, and those potential impactors are most worrisome as they may cause widespread fatalities. The dinosaurs suffered a mass-extinction owing, at least in large part, to a 10-km impactor that struck Earth 65 million years ago. However, Mainzer notes that the survey completeness drops to 25% for nearby 100-m asteroids, and it is likely to be less than 1% for 20-m asteroids like that which exploded over Russia (Chelyabinsk). The Tunguska event (see the image below) is likewise speculated to have been on the order of that latter size.
In 1908 the Tunguska meteor explosion toppled millions of trees in a rather remote part of Siberia. A new study by Mainzer et al. 2013 characterized 100+ objects lurking in the vicinity of the Earth that are on the order of the Tunguska impactor.
The team highlights that approximately 10,000 near-Earth objects have been discovered to date, 900 of which are 1-km or larger, and 3500 objects appear to be 100-m or smaller. “Because their small sizes usually make them undetectable until they are very nearby the Earth, it is often difficult for the current suite of asteroid surveys and follow-up telescopes to track them for very long.
Consequently, the fraction of the total population at small sizes that has been discovered to date remains very low,” noted Mainzer.
In closing, Mainzer emphasizes that, “It is, however, clear that much work remains to be done to discover and characterize the population of very small NEOs [near-Earth objects].”
The Mainzer et al. 2013 findings have been accepted for publication in the Astrophysical Journal (ApJ), and a preprint is available on arXiv. Coauthors on the study are J. Bauer, T. Grav, J. Masiero, R. M. Cutri, E. L. Wright, C. R. Nugent, R. Stevenson, E. Clyne, G. Cukrov, and F. Masci.
Beautiful red and green aurora the night of Oct. 1-2, 2013. See below for how it appeared to the eye. Details: 20mm lens, f/2.8, ISO 1600 and 25-second exposure. Credit: Bob King
I shoot a lot of pictures of the northern lights. Just like the next photographer, I thrill to the striking colors that glow from the back of my digital camera. When preparing those images for publication, many of us lighten or brighten the images so the colors and forms stand out better. Nothing wrong with that, except most times the aurora never looked that way to our eyes.
Surprised? I took the photo above and using Photoshop adjusted color and brightness to match the naked eye view. Notice the green tinge in the bright arc at bottom. The rays were colorless. Credit: Bob King
The colors you see in aurora photos ARE real but exaggerated because the pictures are time exposures. Once the camera’s shutter opens, light accumulates on the electronic sensor, making faint and pale subjects bright and vivid. The camera can’t help it, and who would deny a photographer the chance to share the beauty? Most of us understand the magic of time exposures and factor in a mental fudge factor when looking at astronomical photos including those of the aurora.
But photos can be misleading, especially so for beginners, who might anticipate “the second coming” when they step out to watch the northern lights only to feel disappointment at the real thing. Which is too bad, because the real aurora can make your jaw drop.
A massive wall of bright purple and green rays from July 20, 2012. Details: 16mm at f/2.8, ISO 800 and 20 second exposure. Credit: Bob King
That’s why I thought it would instructive to take a few aurora photos and tone them down to what the eye normally sees. Truth in advertising you know. I’ve also started to include disclaimers in my captions when the images show striking crimson rays. Veteran aurora watchers know that some of the most memorable auroral displays glow blood-red, but most of the ruddy hues recorded by the camera are simply invisible to the eye. Our eyes evolved their greatest sensitivity to green light, the slice of the rainbow spectrum in which the sun shines most intensely. We’re slightly less sensitive to yellow and only a 1/10 as sensitive to red.
Image adjusted to better represent the visual view. Most auroras are between 60 and 150 miles high, but occasionally reach to 400 miles. Credit: Bob King
A typical aurora begins life as a pale white band low in the northern sky. If we’re lucky, the band intensifies, crosses the color threshold and glows pale green. Deeper and brighter greens are also common in active and bright auroras, but red is elusive because are eyes are far less sensitive to it than green. Often a curtain of green rays will be topped off by red, blue or purple emission recorded with sumptuous fidelity in the camera. What does the eye see? Smoky, colorless haze with hints of pink. Maybe.
Again, this doesn’t mean we only see green and white. I’ve watched brilliant (pale) green rays stretch from horizon to zenith with their bottoms bathed in rosy-purple, a most wonderful sight. Another factor to keep in mind is dark adaption – the longer you’ve been out under a dark sky, the more sensitive your eyes will be to whatever color might be present. At night, however, we’re mostly color blind, relying on our low-light-sensitive rod cells to get around. Cone cells, fine-tuned for color vision, are activated only when light intensity reaches certain thresholds. That happens often when it comes to auroral green but less so with other colors to which our cells are less responsive.
Incoming auroral electrons excite oxygen and nitrogen atoms and molecules which then shoot out photons of light at specific wavelengths when they return to their ground states. Oxygen beams light at 557.7 (green) and 603 (red) nanometers. Credit: NCAR
Auroral colors originate when electrons from the sun spiral down Earth’s magnetic field lines like firemen on a firepole and slam into oxygen and nitrogen atoms in Earth’s upper atmosphere between 60 and 150 miles (96-240 km) high. Here’s a breakdown of color, atom and altitude:
* Green – oxygen atoms 60-93 miles up (100-150 km)
* Red – oxygen atoms from 93-155 miles (150-250 km)
* Purple – molecular nitrogen up to 60 miles (100 km)
* Blue/purple – molecular nitrogen ions above 100 miles (160 km)
When an electron strikes an oxygen atom for instance, it bumps one of the oxygen’s electrons to a higher energy level. When that electron drops back down to its previous rest or ground state, it emits a photon of green light. Billions of atoms and molecules, each cranking out tiny flashes of light, make an aurora. It takes about 3/4 second for that electron to drop and the atom to release a photon before it’s given another kick from a solar electron. Most auroras are rich with oxygen emission.
The layers of our atmosphere showing the altitude of the most common auroras. Credit: Wikimedia Commons
Higher up, where the air’s so thin it’s identical to a hard vacuum, collisions between atoms happen only about every 7 seconds. With lots of time on their hands, oxygen electrons can transition down to their lowest energy level inside the atom, releasing a photon of red light instead of green. That’s why tall rays often show red tops especially in time exposure photos.
Only during very active geomagnetic storms, when electrons penetrate to low levels in the atmosphere, are they able to excite molecules of nitrogen, giving rise to the familiar purple fringes at the bottoms of bright rays. Bombarded molecular nitrogen ions at high altitude release a deep blue-purple light. Rarely visible to the eye, I did record it one night in the camera.
A striking coronal aurora in Feb. 1999 photographed on film. The red in this aurora was obvious to the naked eye but appeared more like the Photoshopped version at right. Credit: Bob King
While videos hint at how wildly dynamic auroras can be, they’re no substitute for seeing one yourself. That’s why I never seem to get to bed when that first tempting glow appears over the northern horizon. Colorful or colorless, you’ll be astonished at how the aurora constantly re-invents itself in a multitude of forms from arcs to rays to flaming patches and writhing curlicues. Don’t miss the chance to see one. If there’s one thing that looks absolutely unearthly on this green Earth, it’s the aurora borealis. Click HERE for a guide on when and where to watch for them.
This question comes from Andrew Bumford and Steven Stormont.
In a previous episode I’ve talked about how the entire Solar System collapsed down from a cloud of hydrogen and helium left over from the Big Bang. And yet, we stand here on planet Earth, with all its water. So, how did that H20 get to our planet? The hydrogen came from the solar nebula, but where did the oxygen come from?
Here’s the amazing part.
The oxygen came from stars that lived and died before our Sun was even born. When those stars puffed out their final breaths of oxygen, carbon and other “metals”, they seeded new nebulae with the raw material for new worlds. We owe our very existence to the dead stars that came before.
When our Sun dies, it’ll give up some of its heavier elements to the next generation of stars. So, mix hydrogen together with this donated oxygen, and you’ll get H20. It doesn’t take any special process or encouragement, when those two elements come together, water is the result.
But how did it get from being spread across the early Solar System to concentrating here on Earth, and filling up our oceans, lakes and rivers? The exact mechanism is a mystery. Astronomers don’t know for sure, but there are a few theories:
Idea #1: impacts. Take a look at the craters on the Moon and you’ll see that the Solar System was a busy place, long ago. Approximately 3.8 to 4.1 billion years ago was the Late Heavy Bombardment period, when the entire inner Solar System was pummeled by asteroids. The surfaces of the planets and their moons were heated to molten slag because of the non-stop impacts. These impactors could have been comets or asteroids.
Comets are 80% water, and would deliver vast amounts of water to Earth, but they’re also volatile, and would have a difficult time surviving the harsh radiation of the young Sun. Asteroids have a lower ratio of water, but they could protect that water a little better, delivering less with each catastrophic impact.
A false-color, visible-light image of Comet ISON taken with Hubble’s Wide Field Camera 3. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Astronomers have also found many hybrid objects which contain large amounts of both rock and water. It’s hard to classify them either way.
Idea #2 is that large amounts of water just came directly from the solar nebula. As we orbited around the young Sun, it passed through the water-rich material in the nebula and scooped it up. Gravitational interactions between the planets would have transferred material around the Solar System, and it would have added to the Earth’s volume of water over hundreds of millions of years.
Of course, it’s entirely possible that the answer is “all of the above”. Asteroids and comets and the early solar nebula all delivered water to the Earth. Where did the Earth’s water come from? Astronomers don’t know for sure. But I’m sure glad the water is here; life here wouldn’t exist without it.
PGC 6240, a petal-like galaxy that probably was altered by a galactic merger. Credit: ESA/Hubble & NASA with acknowledgement to Judy Schmidt
Across the universe, some 350 million light-years away, lies a galaxy that looks like it has white rose petals. Don’t let the tranquil appearance of PGC 6240 fool you as to its past, however. This galaxy in Hydrus (The Water Snake) likely was dramatically altered by a galactic merger.
There’s a bunch of evidence pointing to this. There are “star shells” of globular clusters around the galaxy, but they’re distributed unevenly — some are close in, some are way out in the distant suburbs. Also, “several wisps of material have been thrown so far that they appear to be almost detached from the galaxy altogether,” stated the Hubble European Space Agency Information Centre.
“The most likely explanation for both the galaxy’s stacked shell structure and the unexpectedly young star clusters is that PGC 6240 merged with another galaxy at some point in the recent past,” the agency added.
“Such a merger would send ripples through the galaxy and disrupt its structure, forming the concentric shells of material seen here. It would also ignite a strong burst of star formation in the galaxy, which would then trigger similar activity in nearby space — leading to the creation of new, younger globular clusters around PGC 6240.”
Artist's conception of PSO J318.5-22. Credit: MPIA/V. Ch. Quetz
The planetary world keeps getting stranger. Scientists have found free-floating planets — drifting alone, away from stars — before. But the “newborn” PSO J318.5-22 (only 12 million years old) shows properties similar to other young planets around young stars, even though there is no star nearby the planet.
“We have never before seen an object free-floating in space that that looks like this. It has all the characteristics of young planets found around other stars, but it is drifting out there all alone,” stated team leader Michael Liu, who is with the Institute for Astronomy at the University of Hawaii at Manoa. “I had often wondered if such solitary objects exist, and now we know they do.”
Image from the Pan-STARRS1 telescope of the free-floating planet PSO J318.5-22, in the constellation of Capricornus. Credit: N. Metcalfe & Pan-STARRS 1 Science Consortium
The planet is about 80 light-years from Earth, which is quite close, and is part of a star group named after Beta Pictoris that also came together about 12 million years ago. There is a planet in orbit around Beta Pictoris itself, but PSO J318.5-22 has a lower mass and likely had a different formation scenario, the researchers said.
Astronomers uncovered the planet, which is six times the mass of Jupiter, while looking for brown dwarfs or “failed stars.” PSO J318.5-22’s ultra-red color stood apart from the other objects in the survey, astronomers said.
The free-floating planet was identified in the Pan-STARRS 1 wide-field survey telescope in Maui. Follow-up observations were performed with several other Hawaii-based telescopes, including the NASA Infrared Telescope Facility, the Gemini North Telescope, and the Canada-France-Hawaii Telescope.
The discovery will soon be detailed in Astrophysical Letters, but for now you can read the prepublished verison on Arxiv.
An analysis of the dust coma of comet ISON showing the evaporation of ice particles. (Credit: NASA/ESA J.-Y. Li (Planetary Science Institute and the Hubble ISON Imaging Science Team).
It’s the question on every astronomer’s mind this season, both backyard and professional: will Comet C/2012 S1 ISON survive perihelion?
Now, new studies released today at the American Astronomical Society’s 45th Annual Division for Planetary Sciences meeting being held this week in Denver suggests that ISON may have the “right stuff” to make it through its close perihelion passage near the Sun. This is good news, as Comet ISON is expected to be the most active and put on its best showing post-perihelion… if it survives.
Researchers Matthew Knight of the Lowell Observatory and Research Scientist Jian-Yang Li of the Planetary Science Institute both presented a compelling portrait of the characteristics and unique opportunities presented by the approach of comet ISON to the inner solar system.
Jian-Yang Li studied ISON earlier this year using Hubble before it passed behind the Sun from our Earthly vantage point. Li and researchers were able to infer the position and existence of a jet coming from the nucleus of the comet, which most likely marks the position of one of its rotational poles.
“We measured the rotational pole of the nucleus,” Li noted in a press release from the Planetary Science Institute. The pole indicates that only one side of the comet is being heating by the Sun on its way in until approximately one week before it reaches its closest point to the Sun.”
Could we be in for a “surge” of activity from ISON coming from around November 20th on?
Comet ISON as imaged from Aguadilla, Puerto Rico recently on October 6th. (Credit: Efrain Morales Rivera).
Li also noted that the reddish color of the coma of ISON suggests an already active comet sublimating water ice grains as they move away from the nucleus. He also noted that time has been allocated to observe ISON using Hubble this week.
Next up, researcher Mathew Knight presented some encouraging news for ISON when it comes to surviving perihelion.
The findings were a result of numerical simulations carried out by Kevin Walsh and Knight, combined with a historical analysis of previous sun-grazing comets. Both suggest that comet nuclei smaller than 200 metres in diameter, with an average density or lower (for comets, that is) typically do not survive a close passage to the Sun.
Both researchers place the size of ISON’s nucleus in the range of 0.5 to 2 kilometres, comfortably above the 0.2 kilometre “shred limit” for its relative perihelion distance. ISON is not a technically Kreutz group sungrazer, though studies of the over 2,000 known Kreutz comets historically observed provide an interesting guideline for what might be in store for ISON. Four Kreutz comets, including C/2011 W3 Lovejoy and Comet C/1887 B1 partially survived perihelion to become “headless wonders,” while five, including Comet C/1965 S1 Ikeya-Seki — which ISON is often compared to — survived perihelion passage to become one of the great comets of the 20th century.
ISON will pass inside the Roche limit of the Sun, which is a distance of 2.4 million kilometres (for fluid bodies) and will be subject to temperatures approaching 5,000 degrees Fahrenheit on closest approach.
ISON is a first time visitor to the inner solar system. Discovered on September 21st, 2012 by Russian researchers Artyom Novichonok and Vitaly Nevsky participating in the International Scientific Optical Network, ISON will pass less than 1.2 million kilometres above the surface of the Sun on November 28th, 2013.
One interesting but little discussed factor highlighted in today’s press release was the retrograde versus prograde rotation of the cometary nucleus. A fast, prograde spin of an elongated nucleus may spell doom for ISON, as tidal forces will rip it apart. A retrograde rotator, however, is very likely to survive the encounter.
Thus far, there are no solid indications that ISON is indeed a retrograde rotator, although there are tantalizing hints that beg for further observations.
Li notes that it’s tough to infer a bias for comets like ISON to be retrograde over prograde rotators, as we’ve only got five historical comets to go by similar to ISON, and the breakdown is thus about 50/50 for and against.
ISON’s possible survival would validate both studies and their methods and give us more refined predictions for future comets.
“We’ve never discovered a sungrazer this far out,” Knight told Universe Today. “The rotation of ISON depends on the pole position (from Li’s study) and in theory, if we could get enough images, a proper morphology (for ISON) would emerge.”
Comet ISON imaged on October 5th from Long Beach, California. (Credit: Thad Szabo @AstroThad).
The implications of this analysis is certainly good news for observers. If ISON survives perihelion, we would then have a brilliant dawn Christmas comet unfurling its tail off to the northeast in early December.
Of course, these findings are contrary to early cries of its demise, including the paper out of the Institute of Physics that has been circulating touting “The Impending Demise of ISON”. Read Universe Today editor Nancy Atkinson’s excellent synopsis on that, it’s a tale that just won’t seem to die.
And we’ve also done our skeptic’s duty of thoroughly debunking the mounting ISON lunacy, including its status as the harbinger for the “end of the world of the week,” as well as its inability to fulfill prophecy. But if we get a surge in ISON next month as researchers suggest, we fully expect the accompanying hype to crest as well.
The most recent observations put ISON at about +10th magnitude as it currently crosses the constellation Leo, near Mars and Regulus in the morning sky. We recently did an observing post tracking its plunge to perihelion in late November, and we’ve been diligently hunting for ISON with binoculars every morning pre-dawn.
We’re glad to have some positive science to report on for ISON. Things are looking up for a fine show come early December!
-Read the PSI press release on JianYang Li’s findings as well as the original paper on ISON’s survival prospects by Matthew Knight.
An artist's conception of two magnetic fields interacting in a bow shock. Image credit: NASA
Astronomers may soon be able to observe the shockwaves between the magnetic fields of exoplanets and the flow of particles from the stars they orbit.
Magnetic fields are crucial to a planet’s (and as it turns out a moon’s) habitability. They act as protective bubbles, preventing harmful space radiation from stripping away the object’s atmosphere entirely and even reaching the surface.
An extended magnetic field – known as a planetary magnetosphere – is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge. Within our own Solar System, Jupiter’s magnetosphere extends to distances up to 50 times the size of the planet itself, nearly reaching Saturn’s orbit.
When the wind of high-energy particles from the star hits the planetary magnetosphere, it interacts in a bow shock that diverts the wind and compresses the magnetosphere.
Recently a team of astronomers, led by PhD student Joe Llama of the University of St. Andrews, Scotland, have worked out how we might observe planetary magnetospheres and stellar winds via their bow shocks.
Llama took a careful look at the planet HD 189733b, located 63 light years away toward the constellation Vulpecula. From the Earth, the planet is seen to transit its host star every 2.2 days, causing a dip in the overall light from the system.
As a bright star, HD 189733b has been studied extensively by astronomers. Data collected in July 2008 by the Canada-France-Hawaii telescope mapped the star’s magnetic field. While the magnetic field varied, it was on average 30 times greater than that of our Sun – meaning that the stellar wind is much higher than the solar wind.
This allowed the team to carry out extensive simulations of the stellar wind around HD 189733b – characterizing the bow shock created as the planet’s magnetosphere passes through the stellar wind. With this information they were able to simulate the light curves that would result from the planet and the bow shock orbiting the star.
The bow shock leads the planet – causing the light to drop a little earlier than expected. The amount of light blocked by the bow shock, however, will change as the planet moves through a variable stellar wind. If the stellar wind is particularly strong, the resulting bow shock will be strong, and the transit depth will be greater. If the stellar wind is weak, the resulting bow shock will be weak, and the transit depth will be less.
The video below shows the light curve of a bow shock and exoplanet.
“We found that the shockwave between the stellar and planetary magnetic fields will change drastically as activity on the star varies,” Llama told Universe Today. “As the planet passes through very dense regions of the stellar wind, so the shock will become denser, the material in it will block more light and therefore cause a larger dip in the transit making it more detectable.”
While there were no transit observations for this study, this theoretical outlook demonstrates that it will be possible to detect the bow shock, and therefore the magnetic field, of a distant exoplanet. Dr. Llama comments: “This will help us to better identify potentially habitable worlds.”
The paper has been accepted for publication in Monthly Notices of The Royal Astronomical Society and is available for download here.
