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.
Up for a challenge? Got a big 12” light bucket of a Dobsonian telescope and looking for something new to point it at? This week, as the Moon reaches New phase on October 4th and stays safely out of the late evening sky, why not check out Uranus and its retinue of moons. And yes, we’ve heard just about ALL the Uranus jokes —its pronouncedyer-in-us, thank you very much — but feel free to attempt to pen an original if you must.
Now, back to astronomy. Uranus reaches opposition for 2013 on Thursday, October 3rd at 14:00 Universal Time. Opposition is the point in time that an outer planet rises as the Sun sets. In the case of Uranus, its opposition dates advance forward by about 4-5 days each year.
The current location of Uranus in Pisces. Created by the author using Stellarium. (click to enlarge).
This also marks the start of the best time to hunt for the planet among the star fields of the constellation Pisces. Uranus will reach its maximum elevation above the southern horizon for northern hemisphere viewers for early October around local midnight. For observers south of the equator, Uranus will transit to the north. Incidentally, Uranus also currently sits near the equinoctial point occupied by the Sun during the March equinox, making viewing opportunities nearly equal for both hemispheres.
Uranus is 19.04 astronomical units distant during opposition 2013, or about 158 light minutes away. Shining at magnitude +5.8, Uranus presents a tiny blue-green disk just under 4” across at opposition.
Uranus currently lies six degrees SW of the +4.4 magnitude star Delta Piscium, on the border of the constellations Pisces and Cetus. Uranus will actually be crossing once again into the non-zodiacal constellation of Cetus later this year.
Discovered in 1781 by Sir William Herschel, Uranus has only completed 2 full orbits (2.75 to be precise) in its 84.3 year trips about the Sun. We can be thankful that William’s proposal to name the planet Geogium Sidus after his benefactor King George the III didn’t stick!
The path of Uranus into Cetus. Created by the author using Starry Night Education software.
At opposition, Uranus will be located at;
Right Ascension: 0h 40’
Declination: +3° 25’
Five of the 27 known moons of Uranus are also within the grasp of a moderate-sized backyard scope as well. The trick is to catch ‘em near greatest elongation, when they appear farthest from the “glare of Uranus” (hey, there’s a freebie for a snicker or two). An eyepiece equipped with an occulting bar, or simply nudging Uranus out of the field of view can also help.
With magnitudes ranging from +13 to +16, the moons of Uranus are similar in brightness to Neptune’s large moon Triton or the tiny world Pluto.
The five brightest moons of Uranus and their respective maximum elongations are:
Chart constructed by author.
And here’s a handy finder chart for the coming month, showing maximum elongations for each:
A corkscrew graph featuring the greatest elongations for the five brightest moons of Uranus through October. (Created by Ed Kotapish using PDS Rings Node).
The first two moons were named Titania and Oberon by William’s son John after characters from William Shakespeare’s A Mid-Summer Night’s Dream. William discovered the first two moons of Uranus on the night of January 11th, 1787 using his 49.5” reflector. His scopes were so advanced for his day, that it wasn’t until over a half a century later that William Lassell discovered Umbriel and Ariel using the Liverpool Observatory’s 24” reflector in 1851.
Gerard Kuiper would later add tiny Miranda to the list, nabbing it with the McDonald Observatory’s 82” Otto Struve Telescope in 1948. We would then have to wait until Voyager 2’s 1986 flyby of Uranus in 1986 to add more. To date, Voyager 2 remains the only spacecraft to visit Uranus and Neptune.
The current convention established by the International Astronomical Union is to name the moons of Uranus after characters from the plays of Shakespeare or Alexander Pope’s Rape of the Lock.
There’s still a wide range of names in said literature to choose from!
It’s interesting to note that the orbits of the moons of Uranus are also currently tipped open about 25 degrees to our line of sight and widening. They were edge on in December 2007, and will be perpendicular to our Earthly view come 2029, after which they’ll head back to edge on in 2049. This is because Uranus and the orbits of its moons are tipped at a 97 degree angle relative to the planet’s orbit. This is why elongations for its moons are often quoted it terms of “north and south” of the planet, rather than the familiar east and west. Shadow transits of the moons can occur with about a year and a half during plane-crossing seasons, but they’re ~42 years apart and tough to spot on the tiny disk of Uranus!
An example of the orientation of Uranus’s moons on October 4th, with Oberon at greatest elongation. Note that Miranda is the tiny unlabeled moon with the interior orbit. (Created by the author using Starry Night Education software).
Uranus also reached aphelion in 2009 at 20.099 AU from the Sun —we’re still at the farther end of the spectrum, as oppositions of Uranus can range from 19.09 to 17.28 AU distant.
Uranus will rise earlier on each successive evening until it reaches quadrature at the end of the year on December 30th. At this point, it’ll be roughly due south at local sunset. Keep in mind, there’s also another ice giant worth hunting for in the adjacent constellation of Aquarius named Neptune.
So ignore those bad puns, and be sure to take out that 10” (scope, that is) and point it at Uranus!
A DVD bound for Mars... (Courtesy of Lockheed Martin/LASP).
Fans of Mars and spaceflight waxed poetic as the haiku selected to travel to Mars aboard the MAVEN spacecraft were announced earlier this month.
The contest received 12,530 valid entries from May 1st through the contest cutoff date of July 1st. Students learned about Mars, planetary exploration and the MAVEN mission as they composed haiku ranging from the personal to the insightful to the hilarious.
“The contest has resonated with people in ways that I never imagined! Both new and accomplished poets wrote poetry to reflect their views of Earth and Mars, their feelings about space exploration, their loss of loved ones who have passed on, and their sense of humor,” said Stephanie Renfrow, MAVEN Education & Public Outreach & Going to Mars campaign lead.
A total of 39,100 votes were cast in the contest; all entries receiving more than 2 votes (1,100 in all) will be carried on a DVD affixed to the MAVEN spacecraft bound for Martian orbit.
Five poems received more than a thousand votes. Among these were such notables as that of one 8th grader from Denver Colorado, who wrote;
Phobos & Deimos
Moons orbiting around Mars
Snared by Gravity
Another notable entry which was among the poems sited for special recognition by the MAVEN team was that of Allison Swets of Michigan;
My body can’t walk
My mouth can’t make words but I
Soar to Mars today
377 artwork entries were also selected to fly aboard MAVEN as well.
Didn’t get picked? There’s still time to send your name aboard MAVEN along with thousands that have already been submitted. You’ve got until September 10!
Part of NASA’s discontinued Scout-class of missions, the Mars Atmosphere and Volatile EvolutioN mission, or MAVEN, is due to launch out of Cape Canaveral on November 18th, 2013. Selected in 2008, MAVEN has a target cost of less than $500 million dollars US, not including launch carrier services atop an Atlas V rocket in a 401 flight configuration.
The Phoenix Lander was another notable Scout-class mission that was extremely successful, concluding in 2008.
Principal investigator for MAVEN is the University of Boulder at Colorado’s Bruce Jakosky of the Laboratory for Atmospheric and Space Physics (LASP).
The use of poetry to gain public interest in the mission is appropriate, as MAVEN seeks to solve the riddle that is the Martian atmosphere. How did Mars lose its atmosphere over time? What role does the solar wind play in stripping it away? And what is the possible source of that anomalous methane detected by Mars Global Surveyor from 1999 to 2004?
MAVEN is based on the design of the Mars Odyssey and Mars Reconnaissance Orbiter spacecraft. It will carrying an armada of instruments, including a Neutral Gas & Ion Mass Spectrometer, a Particle and Field Package with several analyzers, and a Remote Sensing Package built by LASP.
MAVEN just arrived at the Kennedy Space Center earlier this month for launch processing and mating to its launch vehicle. Launch will be out of Cape Canaveral Air Force Station on November 18th with a 2 hour window starting at 1:47 PM EST/ 18:47 UT.
MAVEN spacecraft at a Lockheed Martin clean room near Denver, Colo. (Credit: Lockheed Martin).
Assuming that MAVEN launches at the beginning of its 20 day window, it will reach Mars for an orbital insertion on September 22, 2014. MAVEN will orbit the Red Planet in an elliptical 150 kilometre by 6,200 kilometre orbit, joining the Mars Reconnaissance Orbiter, the European Space Agencies’ Mars Express and the aging Mars Odyssey orbiter, which has been surveying Mars since 2001.
The window for an optimal launch to Mars using a minimal amount of fuel opens every 24 to 26 months. During the last window of opportunity in 2011, the successful Mars Curiosity rover and the ill-fated Russian mission Phobos-Grunt sought to make the trip.
This time around, MAVEN will be joined by India’s Mars Orbiter Mission, launching from the Satish Dhawan Space Center on October 21st. If successful, the Indian Space Research Organization (ISRO) will join Russia, ESA & NASA in nations that have successfully launched missions to Mars.
This window comes approximately six months before Martian opposition, which next occurs on April 8th, 2014. In 2016, ESA’s ExoMars Mars Orbiter and NASA’s InSight Lander will head to Mars. And 2018 may see the joint ESA/NASA ExoMars rover and… if we’re lucky, Dennis Tito’s proposed crewed Mars 2018 flyby.
Interestingly, MAVEN also arrives in Martian orbit just a month before the close 123,000 kilometre passage of comet C/2013 A1 Siding Spring, although as of this time, there’s no word if it will carry out any observations of the comet.
These launches will also represent the first planetary missions to depart Earth since 2011. You can follow the mission as @MAVEN2Mars on Twitter. We’ll also be attending the MAVEN Conference and Workshop this weekend in Boulder and tweeting our adventures (wi-fi willing) as @Astroguyz. We also plan on attending the November launch in person as well!
And in the end, it was perhaps for the good of all mankind that our own rule-breaking (but pithy) Mars haiku didn’t get selected:
Rider of the Martian Atmosphere
Taunting Bradbury’s golden-bee armed Martians
While dodging the Great Galactic Ghoul
Hey, never let it be said that science writers make great poets!
An artist's concept of a rocky world orbiting a red dwarf star. (Credit: NASA/D. Aguilar/Harvard-Smithsonian center for Astrophysics).
Hunters of alien life may have a new and unsuspected niche to scout out.
A recent paper submitted by Associate Professor of Astronomy at Columbia University Kristen Menou to the Astrophysical Journal suggests that tidally-locked planets in close orbits to M-class red dwarf stars may host a very unique hydrological cycle. And in some extreme cases, that cycle may cause a curious dichotomy, with ice collecting on the farside hemisphere of the world, leaving a parched sunward side. Life sprouting up in such conditions would be a challenge, experts say, but it is — enticingly — conceivable.
The possibility of life around red dwarf stars has tantalized researchers before. M-type dwarfs are only 0.075 to 0.6 times as massive as our Sun, and are much more common in the universe. The life span of these miserly stars can be measured in the trillions of years for the low end of the mass scale. For comparison, the Universe has only been around for 13.8 billion years. This is another plus in the game of giving biological life a chance to get underway. And while the habitable zone, or the “Goldilocks” region where water would remain liquid is closer in to a host star for a planet orbiting a red dwarf, it is also more extensive than what we inhabit in our own solar system.
Gliese 581- an example of a potential habitable zone around a red dwarf star contrasted with our own solar system. (Credit: ESO/Henrykus under a Wikimedia Creative Commons Attribution 3.0 Unported license).
But such a scenario isn’t without its drawbacks. Red dwarfs are turbulent stars, unleashing radiation storms that would render any nearby planets sterile for life as we know it.
But the model Professor Menou proposes paints a unique and compelling picture. While water on the permanent daytime side of a terrestrial-sized world tidally locked in orbit around an M-dwarf star would quickly evaporate, it would be transported by atmospheric convection and freeze out and accumulate on the permanent nighttime side. This ice would only slowly migrate back to the scorching daytime side and the process would continue.
Could these types of “water-locked worlds” be more common than our own?
The type of tidal locking referred to is the same as has occurred between the Earth and its Moon. The Moon keeps one face eternally turned towards the Earth, completing one revolution every 29.5 day synodic period. We also see this same phenomenon in the satellites for Jupiter and Saturn, and such behavior is most likely common in the realm of exoplanets closely orbiting their host stars.
The study used a dynamical model known as PlanetSimulator created at the University of Hamburg in Germany. The worlds modeled by the author suggest that planets with less than a quarter of the water present in the Earth’s oceans and subject to a similar insolation as Earth from its host star would eventually trap most of their water as ice on the planet’s night side.
Kepler data results suggest that planets in close orbits around M-dwarf stars may be relatively common. The author also notes that such an ice-trap on a water-deficient world orbiting an M-dwarf star would have a profound effect of the climate, dependent on the amount of volatiles available. This includes the possibility of impacts on the process of erosion, weathering, and CO2 cycling which are also crucial to life as we know it on Earth.
Thus far, there is yet to be a true “short list” of discovered exoplanets that may fit the bill. “Any planet in the habitable zone of an M-dwarf star is a potential water-trapped world, though probably not if we know the planet possesses a thick atmosphere.” Professor Menou told UniverseToday. “But as more such planets are discovered, there should be many more potential candidates.”
Hard times in harsh climes-an artist’s conception of the daytime side of a world orbiting a red dwarf star. (Credit: NASA/JPL-Caltech).
Being that red dwarf stars are relatively common, could this ice-trap scenario be widespread as well?
“In short, yes,” Professor Menou said to Universe Today. “It also depends on the frequency of planets around such stars (indications suggest it is high) and on the total amount of water at the surface of the planet, which some formation models suggest should indeed be small, which would make this scenario more likely/relevant. It could, in principle, be the norm rather than the exception, although it remains to be seen.”
Of course, life under such conditions would face the unique challenges. The daytime side of the world would be subject to the tempestuous whims of its red dwarf host sun in the form of frequent radiation storms. The cold nighttime side would offer some respite from this, but finding a reliable source of energy on the permanently shrouded night side of such as world would be difficult, perhaps relying on chemosynthesis instead of solar-powered photosynthesis.
On Earth, life situated near “black smokers” or volcanic vents deep on the ocean floor where the Sun never shines do just that. One could also perhaps imagine life that finds a niche in the twilight regions of such a world, feeding on the detritus that circulates by.
Some of the closest red dwarf stars to our own solar system include Promixa Centauri, Barnard’s Star and Luyten’s Flare Star. Barnard’s star has been the target of searches for exoplanets for over a century due to its high proper motion, which have so far turned up naught.
The closest M-dwarf star with exoplanets discovered thus far is Gliese 674, at 14.8 light years distant. The current tally of extrasolar worlds as per the Extrasolar Planet Encyclopedia stands at 919.
Searching for and identifying ice-trapped worlds may prove to be a challenge. Such planets would exhibit a contrast in albedo, or brightness from one hemisphere to the other, but we would always see the ice-covered nighttime side in darkness. Still, exoplanet-hunting scientists have been able to tease out an amazing amount of information from the data available before- perhaps we’ll soon know if such planetary oases exist far inside the “snowline” orbiting around red dwarf stars.
Read the paper on Water-Trapped Worlds at the following link.
A sequence of 6 consecutive Jupiter-Venus-Mercury conjunction photos taken on May 23 - 28, 2013. Credit and copyright: Joe Shuster.
We’ve shared oodles of great images from the recent planetary conjunction of Jupiter, Mercury and Venus, visible in the evening skies last week. But this video from astrophotographer César Cantú is just plain beautiful. On the evening of May 25, the conjunction of the three planets formed a triangle that moved through the sky, as seen from Big Bear Park in California, USA. César said via Twitter that the “star” effect was create by processing the video or with 4,6 or 8 point star filters.
And we’ve got one more conjunction image to share — actually six.
Joe Shuster from Salem, Missouri had six great evenings of photographing the planetary conjunction, and put them together into one collage. He used a Canon T1i and Nikkon 105mm lens. Lucky guy!
Planets conjunction over Mont-Saint-Michel, Normandy, France on May 26. Credit: Thierry Legault -
www.astrophoto.fr
Triple planets (Venus/Jupiter/Mercury) conjunction over Mont-Saint-Michel, Normandy, France on May 26. Credit: Thierry Legault – www.astrophoto.fr Update: See expanded Conjunction astrophoto gallery below[/caption]
The rare astronomical coincidence of a spectacular triangular triple conjunction of 3 bright planets happening right now is certainly wowing the entire World of Earthlings! That is if our gallery of astrophotos assembled here is any indication.
Right at sunset, our Solar System’s two brightest planets – Venus and Jupiter – as well as the sun’s closest planet Mercury are very closely aligned for about a week in late May 2013 – starting several days ago and continuing throughout this week.
And, for an extra special bonus – did you know that a pair of spacecraft from Earth are orbiting two of those planets?
Have you seen it yet ?
Well you’re are in for a celestial treat. The conjunction is visible to the naked eye – look West to Northwest shortly after sunset. No telescopes or binoculars needed.
Triple conjunction shot on May 26 from a mile high in Payson,Az. 4 second exposure, ISO200, Canon 10D, 80mm f/5 lens. Credit: Chris Schur- http://www.schursastrophotography.com
Just check out our Universe Today collection of newly snapped astrophoto’s and videos sent to Nancy and Ken by stargazing enthusiasts from across the globe. See an earlier gallery – here.
Throughout May, the trio of wandering planets have been gradually gathering closer and closer.
On May 26 and 27, Venus, Jupiter and Mercury appear just 3 degrees apart as a spectacular triangularly shaped object in the sunset skies – which
adds a palatial pallet of splendid hues not possible at higher elevations.
And don’t dawdle if you want to see this celestial feast. The best times are 30 to 60 minutes after sunset – because thereafter they’ll disappear below the horizon.
The sky show will continue into late May as the planets alignment changes every day.
On May 28, Venus and Jupiter close in to within just 1 degree.
And on May 30 & 31, Venus, Jupiter and Mercury will form an imaginary line in the sky.
Triple planetary conjunctions are a rather rare occurrence. The last one took place in May 2011. And we won’t see another one until October 2015.
Indeed the wandering trio are also currently the three brightest planets visible. Venus is about magnitude minus 4, Jupiter is about minus 2.
While you’re enjoying the fantastic view, ponder this: The three planets are also joined by two orbiting spacecraft from humanity. NASA’s MESSENGER is orbiting Mercury. ESA’s Venus Express is orbiting Venus. And NASA’s Juno spacecraft is on a long looping trajectory to Jupiter.
Send Ken you conjunction photos to post here.
And don’t forget to “Send Your Name to Mars” aboard NASA’s MAVEN orbiter- details here. Deadline: July 1, 2013
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Learn more about Conjunctions, Mars, Curiosity, Opportunity, MAVEN, LADEE and NASA missions at Ken’s upcoming lecture presentations:
June 4: “Send your Name to Mars” and “CIBER Astro Sat, LADEE Lunar & Antares Rocket Launches from Virginia”; Rodeway Inn, Chincoteague, VA, 8:30 PM
June 11: “Send your Name to Mars” and “LADEE Lunar & Antares Rocket Launches from Virginia”; NJ State Museum Planetarium and Amateur Astronomers Association of Princeton (AAAP), Trenton, NJ, 730 PM.
May 25 conjunction over Malta. Canon 450D with a 55mm. lens and an exposure of 1/2 second at ISO 200 on a tripod. Credit: Leonard Ellul-MercerMay 26 triple conjunction from Warwick, NY snapped from Canon Rebel, 100mm – 300mm lens. Credit: Pietro CarboniTriple conjunction from Hondo, Texas taken with a Nikon D800 @ ISO 400 and a 2 second exposure with a Nikon 300mm Lens at F/4. Credit: Adrian New Sunset conjunction with fast moving clouds on May 26 through 10 x 50 binoculars from a seashore town -Marina di Pisa, Tuscany, Italy. Credit: Giuseppe Petricca
Caption: Taken on 2013-05-23 from Salem, Missouri. Canon T1i, Nikkor 105mm lens. 297 1/4s at 1s interval. Images assembled by QuickTime Pro. Credit: Joseph Shuster
May 26 sunset conjunction from Princeton, NJ. Credit: Ken Kremer -kenkremer.comTriple Planetary conjunction over Onset MA. Shot with a Nikon d7000 1/200 f 4 iso 100 at 110mm. Credit: Phillip DamianoPanoramic view over Almada City and Lisbon at the Nautical Twilight, with the Full moon rising above the Eastern horizon (right side of the image), while at the same time but in the opposite direction, the planets Venus, Mercury and Jupiter, are aligned in a triangle formation, setting in the Western horizon (left side of the image).In this panoramic picture is also visible the smooth light transition in the sky, with the end of Nautical Twilight and the beginning of Astronomical Twilight (almost night), at right. Facing to North, is visible the great lighted Monument Christ the King and at the left side of it, part of the 25 April Bridge that connects Almada to Lisbon. Canon 50D – ISO200; f/4; Exp. 1,6 Sec; 35mm. Panoramic of 10 images with about 200º, taken at 21h42 in 25/05/2013. Credit: Miguel Claro – www.miguelclaro.comThe triple conjunction of Venus, Mercury and Jupiter as seen over an Arizona desert landscape. Credit and copyright: Robert Sparks.Jupiter, Venus and Mercury triple conjunction seen here reflecting off Chatsworth Lake in Chatsworth, NJ. Jupiter (on the left) was 2.4° from Mercury (upper-right in the sky) and 2.0° from Venus (bottom right in the sky), while Venus and Mercury were 1.9° apart. Venus was at 2.6° altitude. Canon EOS 6D, 105 mm focal length, 1.3 seconds, f/6.3, ISO 800. Credit: Joe Stieber – sjastro.org/Triple conjunction on May 27 with WBZ radio towers south east of Boston. Hampton Hill, Hull, MA. Nikon D3x -iso200- 1.3 sec.at f2.8. Credit: Richard W. Green
Three bright planets gather in the northwestern sky this week. This map shows the sky 30 minutes after sunset from the middle latitudes. Stellarium
Planning a barbecue this weekend? You may want to top it off with a look at three bright planets shuttling about the western sky at dusk. Jupiter, Venus and Mercury gather for nearly a week of delightful alignments including three separate conjunctions staring right now. Mercury and Venus pair up on Friday; Mercury and Jupiter on Sunday and Venus and Jupiter on Monday. All three form a series of ever-changing triangular arrangements as the nights go by.
Three bright planets will highlight the northwestern sky this week and early next. Mercury is shown in pink and Jupiter in yellow. Time is 30 minutes after sunset facing northwest. They’ll be closest together – less than 3 degrees apart – on the night of the 26th. Stellarium
Brightest of the bunch is Venus followed by Jupiter and then Mercury. The key to seeing them all is a clear sky and unobstructed view of the west-northwest horizon. Best time for viewing is a half hour to 45 minutes after sunset. Although the diagrams make the planets look like largish disks, difference in size is a device to show their brightness. Bigger means brighter.
Mercury gradually climbs higher in the coming days, Venus will remain in nearly the same spot and Jupiter slowly drops off toward the horizon. Seeing three planets bunch up isn’t rare, but it is unusual – all the more reason to go for a look if your skies are clear. Alignments like this occur because all 8 planets lie in essentially the same flat plane. As we look across the solar system, sometimes near planets and far planets lie along the same line of sight and appear side-by-side in the sky. They may look close to each other but of course they’re millions of miles apart.
Positions of the planets on May 27. The arrow shows the point of view from Earth. Notice that the line of sight through all three takes our gaze near the sun. That’s why they’re only visible shortly after sunset in a bright sky. Click image to see a cool, interactive planet display. Credit: dd.dynamicdiagrams.com
This week Venus is 154 million miles (248 million km) from Earth, Mercury 113 million (182 million km) and Jupiter a distant 562 million (904 million km). The planet position diagram above will give you a sense of their current arrangement in space.
Whenever you go planet-seeking in bright twilight, I always recommend bringing along a pair of binoculars. They penetrate haze and make finding these bright little dots much easier. Enjoy the show!
A new study describes how the Kepler team aims to remove pseudo-planets from its database. A pseudo-planet can be caused by the superposition of a foreground bright constant target star, and background fainter multiple star systems as shown in the above artist sketch (image credit: regulus36/devianart).
Observations by the Kepler satellite have advanced our knowledge of stars and their orbiting planets, yielding more than 100 confirmed planets and about 3,000 candidates. However, orbiting planets may not be the source for a fraction of those detections.
“There are many things in the sky that can produce transit-like signals that are not planets, and thus we must be sure to identify what really is a planet detected by Kepler,” Stephen Bryson told Universe Today. NASA Ames Research Center scientists Bryson and Jon Jenkins (also at the SETI Institute) are the lead authors on a new paper that aims to identify pseudo-planets detected by Kepler.
Small eclipses present in Kepler brightness measurements for a star (a lightcurve) may be indicative of an orbiting planet blocking light from its host star (see image below). However, under certain circumstances binary stars can mimic that signature.
Consider a Kepler target that is actually a chance superposition of a bright star and a fainter eclipsing binary system, whereby the objects lie at different distances along the sight-line. The figure below illustrates that their combined light can produce a lightcurve that is similar to a transiting planet. The bright foreground star dilutes the typically large eclipses produced by the binary system.
Left, the lightcurve for a star featuring a transiting planet, whereby the planet blocks a minute fraction of the host star’s light (image credit: Institute for Astronomy, University of Hawaii at Manoa). Right, the combined light from a foreground bright star and a fainter eclipsing binary system can mimic a transiting planet (image credit: chart and assembly, D. Majaess – cropped stellar graphics from Collier Cameron 2012, Nature).
“Most of the time these eclipsing binaries are not exactly aligned with our target star,” Bryson added, “and we can carefully examine the pixels to discover that the location of the transit signal is not the target star.” The team developed algorithms to identify pseudo-planets when the stars are individually resolved. Tagging spurious planet detections is important since there are numerous candidates, and yet limited observing time for follow-up efforts.
The team has been refining those algorithms as knowledge of the satellite’s in situ behavior increases. “These algorithms have been developed and used over the last four years. Some details of the techniques in the paper are new and will appear in future versions of the Kepler [software processing] pipeline,” said Bryson.
However, if multiple stars fall within the same pixel they are not individually resolved by Kepler, and a separate approach is required to infer their presence. Consider the example highlighted in the image below, where several stars were unresolved by Kepler yet appear in higher resolution images. The matter is exacerbated in part because Kepler’s spatial resolution is not optimal, and thus multiple stars may be confused as a single object. By contrast, certain ground-based telescopes can achieve ~20 times Kepler’s spatial resolution when adaptive optics are implemented.
High-resolution images (right panel) can reveal stars that were unresolved in lower-resolution images (left panel, e.g., Kepler). Unresolved stars dilute eclipses caused by transiting planets, and in certain cases can strongly bias the derived parameters (image credit: right panel from Adams et al. 2012, arXiv/AJ – left panel, image blurred to provide a lower-resolution glimpse of the target, assembly by D. Majaess).
Adams et al. 2012 obtained high-resolution images of 90 Kepler targets, one of which is highlighted above. That team noted that, “Close companions … are of particular concern … Of the [90 Kepler targets surveyed] 20% have at least one companion within [half a Kepler pixel].” The high-resolution images were acquired via the MMT observatory (shown below) and the Palomar Hale-200-inch telescope.
Obviously, the resolution problem becomes more acute when observing rich stellar fields (high densities), such as near the plane of our Galaxy.
“Background eclipsing binaries account for as many as 35% of all planet-like transit signals when we are looking near the Milky Way, because there are many stars in the background,” Bryson told Universe Today. “When we look away from the Milky Way the fraction of background eclipsing binaries falls to about 10% of all planet-like transit signals because there are far fewer background stars of all types.”
However, regarding Kepler’s coarser resolution Bryson underscored that, “[it is] expected with such a large field telescope.” Kepler’s large field is certainly advantageous, as it permits the satellite to monitor 100,000+ stars over more than 100 square degrees of field.
The adaptive optics (AO) system at the MMT observatory provides astronomers with high-resolution images to search the vicinity of Kepler planet candidates for contaminating stars (image credit: Thomas Stalcup, SPIE).
Radial velocity measurements are an ideal means for evaluating planet candidates (and to help yield the mass). The data are pertinent since velocity shifts occur in the spectrum of the host star owing to the planet’s gravity. However, Adams et al. 2012 note that “Many of these objects do not have … radial velocity measurements because of the amount of observing time required, particularly for small planets around relatively faint stars. Another method is needed to confirm these types of planets … High-resolution images are thus a crucial component of any transit follow-up program.”
Identifying unresolved stars is crucial for yet another reason. Note that the fundamental parameters determined for a transiting planet depend in part on the fraction of the host star’s light that is obscured (the eclipse depth). However, if multiple unresolved stars exist they will contribute to the overall brightness, and hence the observed planet eclipse will be diluted and underestimated (see figure 2, above). Indeed, Adams et al. 2012 note that, “Corrections to the planetary parameters based on nearby [contaminating] stars can range from a few to tens of percents, making high resolution images an important tool to understanding the true sizes of other discovered worlds.”
The case of K00098 is a prime example underscoring the importance of identifying unresolved contaminating stars. K00098 features two rather bright stars that were unresolved and unknown prior to the acquisition of high-resolution images. Consequently, previously determined parameters for that star’s transiting planet were incorrect. Concerning K00098, Adams et al. 2012 remarked that, “for K00098, the dilution [of the eclipse depth] … were substantial: the [planet’s] radius increased by 10%, the mass by 60% … and the density changed by 25% [from that published]. Without high resolution images, we would have had a very inaccurate picture of this planet.”
Low and high-resolution images of stars in the galaxy M33. The bright object detected in the low-resolution image is actually several stars, as indicated by the higher-resolution image (right). A similar effect occurs when comparing Kepler (lower-resolution) and AO images (higher-resolution). A single Kepler target can actually constitute multiple stars seen along the sight-line (image credit: Mochejska et al. 2001, arXiv).
Incidentally, unaccounted for light from unresolved stars isn’t merely a problem for exoplanet studies. The issue is rather pertinent when researching the cosmic distance scale and the Hubble constant (expansion rate of the Universe). Consider the images above which feature the same field in M33. The image exhibited on the left is from a ground-based facility, whereas the higher-resolution image displayed on the right is from the Hubble Space Telescope (HST). The brightest star at the center of the image is a Cepheid variable star, which is a pulsating star that is used to establish distances to galaxies. In turn those distances are subsequently employed to determine the Hubble constant. The HST image reveals stars that are unresolved in the ground-based image, and thus the distance inferred from that observation is compromised since the Cepheid appears (spuriously) brighter than it should be.
“Blending [e.g., added light caused by unresolved stars] leads to systematically low distances to galaxies observed with the HST, and therefore to systematically high estimates of the Hubble constant,” remarked Mochejska et al. 2004. However, there is an ongoing debate concerning the importance of such an effect (Ferrarese et al. 2000, Mochejska et al. 2001).
In sum, numerous groups are developing methods to identify pseudo-planets in the Kepler database. Given the large sample and sizable investment of time required to confirm a planet candidate: such efforts are important (e.g., Bryson et al. 2013). Data from the Kepler mission have helped advance our understanding of stars and their orbiting planets, and more is yet to come. If you’d like to help the Kepler team identify planets around other stars: join the Planet Hunters citizen science project.
Artist's concept of Kepler in action. NASA/Kepler mission/Wendy Stenzel.
Captain Kirk has nothing on the “strange new worlds” the Kepler space telescope has found.
NASA’s planet-probing orbiting observatory launched its quest to find more Earths four years ago this week. Since then, it’s found thousands of planets ranging from ginormous gas giants to tiny rocky worlds that are even smaller than our planet. NASA extended its mission to 2016 last year, putting the telescope into planet-hunting overtime and, we assume, scientists into overdrive.
Along the way, Kepler has revealed some bizarre star systems. Check out some of the weirdest exoplanets Kepler has found so far:
‘Tatooine’ (Kepler-16b)
Kepler-16b. Credit: NASA/JPL-Caltech
“Circumbinary” is the scientific explanation for Kepler-16b’s 2 star-system. But “Tatooine” is the name that took the public by storm (or is that Stormtrooper?) when this world, orbiting two stars, was revealed in 2011. Although it’s named after Luke Skywalker’s home in Star Wars, proving Kepler-16b is habitable would be a bit of a stretch. The planet’s mass is about one-third that of Jupiter, and surface temperatures reach an estimated and frigid -100 degrees Celsius.
Deciphering a tune (Kepler-37b)
Kepler-37b, a moon-sized exoplanet. Credit: NASA/Ames/JPL-Caltech
Scientists found Kepler 37-b through listening to its parent star sing. Seriously. The planet (just slightly larger than our moon) was revealed through measuring oscillations in brightness caused by star-quakes, then converting those to sound. “The bigger the star, the lower the frequency, or ‘pitch’ of its song,” said Steve Kawaler, a research team member from Iowa State University in a past Universe Today interview.
The 6-planet swarm (Kepler-11b, 11c, 11d, 11e, 11f, 11g)
Kepler’s planets displayed by size comparison. The six new planets around Kepler 11 are on the bottom. Image credit: NASA/Wendy Stenzel
It’s sure crowded around the star Kepler-11. There are six planets orbiting in circles smaller than Venus’ orbit around the Sun. Not only that, but five of those planets are even closer to their parent star than Mercury is to our sun. Excited astronomers said the system will rewrite planetary formation theories. “We really were just amazed at his gift that nature has given us,” said Jack Lissauer, co-investigator of the Kepler mission, in 2011. “With six transiting planets, and five so close and getting the sizes and masses of five of these worlds, there is only one word that adequately describes the new finding: Supercalifragilisticexpialidocious.”
The warring siblings (Kepler-36b and 36c)
In this artist’s conception, a “hot Neptune” known as Kepler-36c looms in the sky of its neighbor, the rocky world Kepler-36b. The two planets have repeated close encounters, experiencing a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets, which may promote active volcanism on Kepler-36b. Credit: David A. Aguilar (CfA)
Take a planet the size of Neptune and put it near Earth, and you’d have some scary results. Tides from the constant interaction would raise the water and the ground, causing fissures and no end of local zoning headaches for municipal authorities as the ground shifts, to say the least. Seriously, though, Kepler-36b (the rocky world) comes within less than 5 Earth-Moon distances of Kepler 36-c (a gaseous world about 8 times larger) every 97 days or so. They’ll never crash into each other, but just like young human siblings, they can cause quite a bit of chaos.
The mirror (Kepler-7b)
Kepler 7b, at right, was one of the first planets discovered by Kepler. Credit: NASA
Well, Kepler-7b isn’t quite as reflective as a mirror, but it certainly catches more sunlight than scientists expected. This “hot Jupiter” was among the first planets that Kepler spotted. In 2011, however, it was revealed that its albedo, or reflectivity, flirted with the upper limit for these humongous planets. What’s causing this? Could be clouds, or could be the composition of its atmosphere. Shows we still have a lot to learn about these exoplanets.
A view of Mercury from MESSENGER’s October 2008 flyby (NASA / JHUAPL / Gordan Ugarkovic)
Every now and then a new gem of a color-composite appears in the Flickr photostream of Gordan Ugarkovic, and this one is the latest to materialize.
This is a view of Mercury as seen by NASA’s MESSENGER spacecraft during a flyby in October 2008. The image is a composite of twenty separate frames acquired with MESSENGER’s narrow-angle camera from distances ranging from 18,900 to 17,700 kilometers and colorized with color data from the spacecraft’s wide-angle camera. (North is to the right.)
Click the image for a closer look, and for an even bigger planet-sized version click here. Beautiful!
The images that made up this mosaic were taken two and a half years before MESSENGER entered orbit around Mercury on March 19, 2011 UT, becoming the first spacecraft ever to do so and making Mercury the final “classical” planet to be orbited by a manmade spacecraft.
Since that time MESSENGER has completed well over 1,000 orbits and taken more than 100,000 images of the first planet in the Solar System, which filled in most of our gaps in Mercury’s map and showed us many never-before-seen features of the planet’s Sun-scoured surface. And just this past year MESSENGER’s extended mission helped confirm what could be called its most important discovery of all: water ice on Mercury’s north pole.
With all that’s been achieved by MESSENGER in 2011 and 2012, 2013 is looking to be an interesting year!
“We learned a great deal about Mercury over the past year,” said MESSENGER Principal Investigator Sean Solomon of Columbia University’s Lamont-Doherty Earth Observatory. “The team published three dozen scientific and technical papers and delivered more than 150 presentations at national and international meetings. New measurements continue to stream back from our spacecraft, and we can look forward with excitement to many additional discoveries in 2013.”
