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Dim Star Has Seven Earth-Size Planets

Wed, 02/22/2017 - 10:05

Astronomers have found seven likely rocky planets around a cool red dwarf, all of which have the potential for liquid surface water.

illustration of TRAPPIST-1 planet sky

Artist’s concept of what the sky might look like from one of the seven known terrestrial planets in the TRAPPIST-1 system.
ESO / M. Kornmesser

The star TRAPPIST-1 is an unassuming, M8 red dwarf star. It lies 39 light-years away in the constellation Aquarius. With a diameter only one-tenth that of our star, the dwarf puts out less than a thousandth as much light as the Sun.

Last year, Michaël Gillon (University of Liège, Belgium) and colleagues announced that a trio of small exoplanets orbits this pipsqueak star (although the third world was of dubious reality). Now, after an intensive follow-up campaign, the team has discovered that there are actually seven planets, not three. All are likely rocky. Three lie in TRAPPIST-1’s putative habitable zone — the region where, given an Earth-like composition, liquid water could be stable on the surface. But all, with enough hand-waving, might have a chance at liquid water.

From Three to Seven triple transit of Trappist-1

This plot is a light curve, showing how the brightness of the faint dwarf star TRAPPIST-1 varies as three of its planets pass across its face in a triple transit on December 11, 2015. Data come from the HAWK-I instrument on ESO’s Very Large Telescope. All three planets are probably rocky, and e and f are in the star's habitable zone.
ESO / M. Gillon et al.

The astronomers detected the exoplanets using the transit technique, which catches the tiny dip in starlight when a planet passes in front of its host star from our perspective. The discovery roller-coaster began when the team found that what it had thought was a combined transit of planets #2 and #3 was in fact the crossing of three planets.

The observers next assailed TRAPPIST-1 with an impressive flurry of ground-based observations. But the big breakthrough came with the Spitzer Space Telescope, which observed the star for 20 days. These data caught 34 clear transits. The team was then able to combine their ground- and space-based observations and slice and dice them to determine that the signals likely came from seven different planets.

Only six of those are firm detections, however. Number 7, or planet h, is iffy in its specs: The team only detected a single transit for it, and astronomers prefer to see three transits before calling something a candidate planet. Expect astronomers to haggle over this one in months ahead.

Mini Solar System? orbit comparisons for solar system and TRAPPIST-1

All of the seven exoplanets discovered around TRAPPIST-1 orbit much closer to their star than Mercury does to the Sun, as shown here in this comparison of the TRAPPIST-1 orbits with the Galilean moons of Jupiter and the planets of the inner solar system. But because TRAPPIST-1 is far fainter than the Sun, the worlds are exposed to similar levels of irradiation as Venus, Earth and Mars.
ESO / O. Furtak

Let’s assume for now that all seven exoplanets are real. All their orbits would easily fit inside Mercury’s circuit around the Sun. Their years range from 1.5 to 12 Earth days long, with the period of outermost h being anywhere between 14 to 35 days. The smallest two worlds are about three-fourths as wide as Earth, the largest 10% wider. The biggest orbit is less than 20% as large as Mercury’s.

One of the wonderful things about this system is that the exoplanets’ orbits are resonant with one another. This means that their orbital periods are rough integer multiples of one another — for example, in the same span of time that the innermost planet whips around the star eight times, the second planet takes five laps, the third three, and the fourth two. This setup gravitationally links the planets together and can lead to tiny shifts in their positions. Based on these shifts, the team could calculate the planets’ gravitational influences on one another, and hence their approximate masses and densities. All are consistent with being rocky, the team concludes in the February 23rd Nature.

Such resonant orbits arise when worlds migrate from their original locations, Gillon explains. Astronomers think that when lightweight planets form far out in a star’s planet-forming gaseous disk, gas drag and such will make them advance inward. During this inbound migration, the worlds catch one another in resonant orbits, such that they can form a kind of “chain of planets,” he says. In this case, the migration landed the exoplanets in what the team calls the “temperate zone” — orbits with enough incoming starlight that, with the right conditions, the planets might at least sometimes have liquid surface water. It’s a looser definition than that for “habitable zone.”

The planets are also all likely tidally locked with their star, meaning they always point the same hemisphere at it, as the Moon does to Earth. So close to the star, the planets could experience huge tidal pulls, stretching and squeezing their interiors and spurring heating and even volcanism, similar to what we see on Jupiter’s Galilean moons.

TRAPPIST-1 is quiet for an M dwarf — notably less active that Proxima Centauri, which also has a habitable-zone planet (although it’s likely a desert world). But unfortunately, astronomers don’t know how old the star is. It’s also unclear whether the planets’ orbits are stable: the researchers haven’t determined the seventh planet’s orbit, nor do they know if there are other worlds in the system mucking things up.

This kind of star, called an ultra-cool dwarf, is very common; roughly 15% of stars in the nearby galaxy fall into this category, Guillon estimates.

Are These Worlds Habitable? trappist-1 orbits

This diagram shows the relative sizes of the orbits of the seven planets orbiting the ultra-cool dwarf star TRAPPIST-1. The shaded area is the habitable zone. Although drawn here, the orbit of the outermost planet, TRAPPIST-1h, is not currently well known. The dotted lines show alternative limits to the habitable zone based on different theoretical assumptions.
ESO / M. Gillon et al.

The next goal is to look at the exoplanets’ atmospheres. If any of the worlds host life, then it might leave chemical fingerprints in the atmospheres. There’s no single compound that’s a smoking gun — for example, oxygen can come from life or from water molecules broken up by starlight into their constituent hydrogen and oxygen atoms. But certain combinations of chemical compounds (such as methane, carbon dioxide, and molecular oxygen) would be highly suggestive.

The team is developing a program to use the Hubble Space Telescope to look at the starlight passing through the planets’ (maybe extant) atmospheres as they transit, to detect any compounds that might have absorbed light. Follow-up will come with the James Webb Space Telescope, which will be more apt for this project because it focuses on infrared wavelengths, and TRAPPIST-1 puts out most of its light in infrared.

Study coauthor Amaury Triaud (Institute of Astronomy, UK) favors planet f as the most promising for life. With a girth of 1.05 Earth radii and about 60% Earth’s density, TRAPPIST-1f might be rich in water and/or ice. It receives about as much energy from its star as Mars does from the Sun, and with a good atmosphere it could be habitable. (Mars is technically in the Sun’s habitable zone.)

During a press conference Triaud painted this picture of what we might see, were we to stand on one of these worlds:

The amount of light reaching your eye would be something like 1/200 as much as you receive from the Sun on Earth — similar to what you experience at the end of sunset. However, it’d still be quite warm, because there’s still about the same amount of energy reaching you from the star as Earth receives from the Sun — it’s just that most of that comes in infrared, which you can’t see but your skin can feel. The star would be a salmon-like color. On TRAPPIST-1f, he estimated, the star would be three times wider in the sky than the Sun is to us.

“The spectacle would be beautiful,” he said.


Read more about the result in the European Southern Observatory’s press release.


M. Gullion et al. “Seven temperate terrestrial planets around the nearby ultracool drwarf star TRAPPIST-1.” Nature. February 23, 2017.

Ignas Snellen. “Earth’s Seven Sisters.” (editorial) Nature. February 23, 2017.

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Categories: Astronomy Headlines

Three Crescents and a Sinking Comet

Wed, 02/22/2017 - 07:10

If you're crazy about crescents, you'll find your happy place this week between the Moon and Venus. Meanwhile, we shift our focus from 45P/H-M-P to another famous periodic comet, 2P/Encke.

Razor's Edge

In Pearce, Arizona, Matt BenDaniel recorded the Moon at dawn on October 15, 2001, only 30.8 hours before new.

What makes a crescent special? Is it the contrast of pointed horns and bowed arc or simply the Moon's fragile appearance that's so breathtaking? If I could find the bumper sticker, I'd happily slap I Brake For Crescents on the back of my car.

Late February crescendos with crescents — two brought to us by the Moon and one via Venus. On Friday morning, February 24th, face southeast about 40 minutes before sunrise to spy a sliver Moon not two days from new with its back to the Sun. Low altitude may color the crescent peach, adding to the beauty of the sight.

Three nights later on February 27th, watch for an even thinner Moon to materialize low in the western sky less than a day and a half past new, horns pointed up and ready to charge into the night like a Pamplona bull.

Crescent Exits Stage East

To begin your crescent catching, find a location with a good view toward the southeastern horizon. This map shows the sky Friday morning and an ~40-hour-old waning crescent Moon.

In late February, the ecliptic arcs sharply up and away from the western horizon, which gives the Moon a swift kick into the evening sky and makes sighting the young crescent easy work.

Opposing Crescents

We'll be able to see opposing crescents — and the ghostly earth-lit disk — in the span of just three days later this week and early next.
Virtual Moon Atlas / C. Legrand & P. Chevalley

Since phases of the Moon and the Earth — as seen from the Moon — are complementary, a sickle Moon implies a nearly full Earth for an astronaut staring back in our direction. Earth, being nearly four times as large as the Moon appears in our sky, reflects a great deal of sunlight back at the Moon, lighting up the remainder of the lunar disk in an ember-like luminescence called earthshine. Earthshine is most obvious when the Moon mimics that Mona Lisa smile.

Lunar Lookalike

Venus cuts a cool crescent in this photo taken on February 20th by Shahrin Ahmad of Sri Damansara, Malaysia. The planet was 28% illuminated at the time.

Venus throws its scimitar in the ring, too! Since greatest eastern elongation in mid-January, Venus has been slimming down while also growing in apparent size as it approaches inferior conjunction on March 25th. Currently a banana-thick crescent measuring 43″ from tip to toe, the planet is large enough to show a shape in any telescope, even 10× binoculars.

The crescent will become larger and strikingly thinner in the coming weeks, so be sure to keep an eye on it. Just like the Moon, the Venusian crescent will flip from one side of the planet to the opposite when it reappears west of the Sun in the morning sky in late March.

Now that I've dragged you by the horns this far, you'll be happy to know there's more than one reasonably bright evening comet vying for your attention. We've been tracking 45P/Honda-Mrkos-Pajdusakova for the past couple weeks, and while it's still just visible in binoculars and now sports a short tail, periodic comet 2P/Encke has been slowly brightening at the same time. Pity it's only now reaching magnitude +9 and soon will be departing the evening sky.

Tuning-Fork Comet

In what has to be one of the most interesting tails ever to be photographed on a comet, this view of 2P/Encke was made on February 16th and shows a bright, compact coma, a faint "tuning fork" tail to the upper right, and dust in the plane of the comet's orbit at lower left. Amazing!
Damian Peach

As I write this, the comet is cozying up to Venus in Pisces, a compact fuzzy glow of magnitude +8.8. It's brightening as it runs westward toward the Sun and will reach perihelion on March 10th. Comet 2P/Encke could become as bright as magnitude +6.5 in the next 10 days and become visible in binoculars shortly before disappearing in the solar glow around March 6th. The best time to catch it is near the end of evening twilight. On February 27th, the thin lunar crescent and Venus will neatly frame the comet. Photos anyone?

Quickly Bright, Then Out of Sight

Use this map, which shows Comet 2P/Encke's nightly position (7 p.m. CST) from February 22nd through March 7th. Stars are shown to magnitude +8 and north is up. Click for a large version to save and print out.
Created with Chris Marriott's SkyMap

Meeting of Three

On February 27th, watch for two crescents to frame Comet 2P/Encke.
Map: Bob King, Source: Stellarium

For northern hemisphere observers, that's all she wrote, but southern skywatchers will have another go at 2P/Encke when it returns to the morning sky in late March at magnitude +8 and fading.

Magnificent Portrait

Comet 45P/H-M-P with a huge coma and broad tail sails past the Whale Galaxy (NGC 4631, at right) and the Hockey Stick Galaxy (NGC 4656) on February 19th.
José J. Chambó

And of course don't forget 45P/Honda-Mrkos-Pajdusakova. Now that it's become well placed in a moonless sky, amateur astronomers have been having better luck recording new details, including a fresh, new tail. The photo above, taken by José J. Chambó, perfectly captures the comet's ethereal beauty in the context of deep space.

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Categories: Astronomy Headlines

Mornington Peninsula Astronomical Society

Tue, 02/21/2017 - 07:32

Mornington Peninsula Astronomical Society


The Briars
Mount Martha, Victoria


David Rolfe


+61 4 13610626






MPAS is approaching 50 years and welcomes members from all over the world to our observing site, located on the outer edge of Melbourne, Victoria, Australia.

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Categories: Astronomy Headlines

Juno Will Stay in Current Orbit Around Jupiter

Tue, 02/21/2017 - 07:22

NASA has announced that its Juno mission will remain in a wide-ranging path around Jupiter.

Jupiter's south pole

Stormy times over Jupiter's southern pole. This image was captured by JunoCam on February 2, 2017, from a range of 62,800 miles (101,000 kilometers).
NASA / JPL-Caltech / SwRI / MSSS / John Landino

NASA has decided to leave the Juno spacecraft in its current 53-day orbit around Jupiter for the remainder of the mission. The decision follows the discovery of a possible engine malfunction in October 2016. Maintaining a wide-ranging orbit will allow the spacecraft's instruments to safely complete the mission's science objectives, while avoiding the risk of another engine malfunction stranding the spacecraft in an unplanned orbit.

“Juno is healthy, its science instruments are fully operational, and the data and images we've received are nothing short of amazing,” says Thomas Zurbuchen (NASA-Science Directorate) in a recent press release. “The decision to forego the burn is the right thing to do — preserving a valuable asset so that Juno can continue its exciting journey of discovery.”

Launched on August 5, 2011, atop an Atlas 5 rocket from Cape Canaveral Air Force Station, Juno entered its initial and current orbit on July 4, 2016. The plan was to make two wide initial capture orbits around Jupiter, burning the main engine on October 19, 2016, to enter a series of 34 shorter, 14-day science orbits.


The original plan for NASA's Juno spacecraft, with two initial capture orbits versus the final phase of science orbits.

However, the unexpected occurred last October: Juno went into safe mode following what was to be the final firing of the spacecraft's main engine. Telemetry later indicated that a pair of helium check valves in the main engine took several minutes to open, longer than on previous firings.

Saving Juno

Engineers analyzed the situation and decided that the best bet was for the spacecraft to stay put, rather than risk another firing of the main engine. Juno will still be able to accomplish its main mission objectives, including probing the magnetosphere, radiation belts, and the gas giant's deep interior. It will now focus on documenting the far reaches of the planet's magnetic field as well. Also, the quality of the data gathered on each pass will remain the same, as the closest passage on the current orbit is identical to those on the hoped-for science orbits. The only difference now is the span of time between passes.

Juno's current orbit takes it from a perijove (closest approach) of just 2,600 miles (4,100 kilometers) over the Jovian cloud tops, to far out past the orbit of Callisto with an apojove of 8.1 million miles (5 million kilometers) distant.

Juno has completed four orbits of Jupiter thus far, giving us some amazing never-before-seen views of the planet's polar regions, and we're expecting to see some of the first science papers using this data in the coming months. Citizen scientists are also making good use of images provided by JunoCam, presenting us with some compelling views.

Juno approaches Jupiter

Jupiter as seen by Juno's JunoCam on first approach last August.
NASA / JPL-Caltech / SwRI / MSSS

The next perijove pass is set for March 27, 2017.

There's another silver lining to the engine anomaly, as Juno may get a brief reprieve before its grand finale. The original plan called for the mission to terminate by entry into Jupiter's atmosphere about a year from now, in February 2018. Juno receives a large amount of radiation on each successive pass, degrading the instruments and spacecraft controls. Engineers planned for a controlled entry in order to protect Jovian moons, such as Europa, from contamination. Orbital precession also carries Juno deeper into Jupiter's radiation belts on each successive pass. Now, NASA plans to operate the mission through July 2018, for a total of 12 orbits, before proposing for a mission extension.

The extended orbit might just be good news after all, as Juno gets a longer rest period between successive doses of instrument damaging radiation. In the end, Juno's loss of an operable main engine might just be science's gain.

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Categories: Astronomy Headlines

The Wizard Nebula (HOO bicolor)

Tue, 02/21/2017 - 00:45

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Categories: Astronomy Headlines

Constellation Glassware from UncommonGreen

Mon, 02/20/2017 - 08:11


Constellation glassware from theUncommonGreentheUncommonGreen now produces a series of etched glassware. The Constellation Glassware series features pints ($16), rocks ($14), and stemless wine glasses ($15) etched with the classical constellations of the Northern Hemisphere’s winter or summer skies. Each is meticulously engraved with the familiar lines and names of the constellations and designed to never wear off. Free shipping on orders of $75 or more.'s New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Sky & Telescope assumes no responsibility for the accuracy of vendors statements. For further information contact the manufacturer or distributor. Announcements should be sent to Not all announcements will be listed.

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Categories: Astronomy Headlines

Comet 45P sails in the dark

Mon, 02/20/2017 - 04:11

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Active Black Hole Encourages Starbirth

Mon, 02/20/2017 - 03:00

Astronomers have discovered long filaments of cold gas — the ingredient for making stars — cocooning giant bubbles inflated by a black hole.

The central galaxies in big clusters are thought to be bereft of stellar nurseries. They’re bathed in hot, X-ray-emitting gas, too superheated to form cool, star-forming clouds. The likely thermostat regulator in this setup is the galaxy’s gas-gobbling central black hole, which blasts out jets and radiation like a tempestuous radiator.

Phoenix galaxy's bubbles and filaments

This composite image shows the environment around the central galaxy in the Phoenix Cluster. The blue glow is X-ray-emitting hot gas. The two black regions inside the glow are huge bubbles in the gas, inflated by the galaxy's active black hole. Filaments of cold gas (pinkish) detected by ALMA seem to hug the bubbles' edges. The background image is from the Hubble Space Telescope.
Radio: ALMA (ESO / NAOJ / NRAO) / H. Russell et al.; Hubble: NASA / ESA Hubble; X-ray: NASA / CXC / MIT / M. McDonald et al.; B. Saxton (NRAO / AUI / NSF)

In 2012, my colleague reported the discovery of cool gas filaments feeding the central galaxy in the Phoenix Cluster, which contains on the order of a thousand stellar metropolises. The galaxy was so gorged with gas that it was churning out about 700 Suns’ worth of stars each year — one of the highest rates in the modern universe. Clearly, when it came to starbirth, this galaxy was a veritable obstetrics ward.

The next course of action was to look at the system with the ALMA radio array, to better assess just how much cold gas was available for star formation.

Members of the original team have now done just that. Reporting in the February 10th Astrophysical Journal, Helen Russell (University of Cambridge, UK) and colleagues found that the galaxy’s black hole is powering intense jets which have inflated huge bubbles of hot gas (visible in X-ray observations). Seemingly wrapped around these cavities are three gigantic filaments of cold, molecular hydrogen gas — the stuff that stars are made of. Each filament is tens of thousands of light-years long.

It’s unclear if the gas clouds were lifted and elongated by the bubbles as they expanded from the galaxy’s core, or if they formed draped this way along the edges due to instabilities in the gas as the hot stuff rose.

Either way, it’s clear that such bubbles sculpt the structure of the largest gas clouds in not only this galaxy but other clusters’ central galaxies, too. Astronomers have seen hints of filament-wrapped cavities before, but not as clearly: the gaseous strands have generally been messier, says Megan Donahue (Michigan State University).

contours of filaments and bubbles

The relationship between the bubbles and filaments is clearer in this intensity map of radio emission (colored contours), with the X-ray cavities shown by the dotted line contours.
H. Russell et al. / Astrophysical Journal 836:130

Donahue’s team has looked at more than two dozen central galaxies as part of the CLASH project, which used the Hubble Space Telescope to study clusters in a whopping 16 wavelengths. The observers have seen very similar filaments in their systems, some even with stars forming inside. Those that are forming stars rank among the most prolific starbirthing galaxies in the universe’s last 5 billion years.

“It’s kind of ironic, because they’re ‘supposed’ to be red and dead,” Donahue says.

Yet the two CLASH galaxies with the largest starburst rates (about 100 solar masses per year) still pale in comparison to the Phoenix’s central galaxy. “Phoenix is an extreme and extraordinary system, so we have to be careful not to think of it as too typical,” she cautions.

Atypical though it may be, the Phoenix system is yet one more result supporting astronomers’ conviction that the gas in these galaxies undergoes a cycle of cooling and heating, controlled by the black hole thermostat. The Phoenix and CLASH galaxies are catching this process in the act.


Read more about the result in NRAO’s press release.


H. R. Russell et al. “ALMA Observations of Massive Molecular Gas Filaments Encasing Radio Bubbles in the Phoenix Cluster.” Astrophysical Journal, February 10, 2017. Full text here.

K. Fogarty et al. “Star Formation Activity in CLASH Brightest Cluster Galaxies.” Astrophysical Journal. Full text here.

Who rules the roost, black holes or galaxies? Find out more in our February 2017 feature.

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Categories: Astronomy Headlines

Eta Carinae Nebula in Narrow Band

Sun, 02/19/2017 - 02:27
Categories: Astronomy Headlines

moon & venus & mars

Fri, 02/17/2017 - 13:14

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Categories: Astronomy Headlines

moon & venus & mars

Fri, 02/17/2017 - 13:14

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Categories: Astronomy Headlines

This Week’s Sky at a Glance, February 17 – 25

Fri, 02/17/2017 - 02:39

Friday, February 17

• The Big Dipper stands on its handle in the northeast around 9 p.m.  In the northwest, Cassiopeia also stands on end at about the same height. As spring approaches, the Dipper will rise higher and Cassiopeia will move lower.

Moon, Saturn, Antares and company in early dawn, Feb. 19-22, 2017 and company

The waning Moon passes over Scorpius, Saturn, and low Sagittarius in early dawn.

Saturday, February 18

• Last-quarter Moon (exact at 2:33 p.m.). Before dawn on Sunday the 19th, look for it in the south-southeast. Antares and upper Scorpius are below and to the lower right of it, respectively. Saturn is farther to the Moon's lower left, as shown here.

Sunday, February 19

• On Monday and Tuesday mornings the 20th and 21st, you'll find Saturn near the waning Moon as shown here.

• This is the time of year when Orion stands highest in early evening. So does Lepus the Hare under his feet. Explore the telescopic deep-sky sights around Lepus's ears (just below Rigel) with Sue French's Deep-Sky Wonders article, chart and photos in the February Sky & Telescope, page 54.

Monday, February 20

• Just 8° west of the Perseus Double Cluster is an interesting binocular star cluster that wasn't even recognized as such until the mid-1950s, and wasn't brought to amateurs' attention until 1977 (though some of us had noticed it independently!). Today it's known as Pazmino's Cluster, a.k.a. Stock 23. See Mathew Wedel's Binocular Highlight column and chart for this and other clusters overshadowed by the famous Perseus pair, in the February Sky & Telescope, page 43.

Tuesday, February 21

• This is a fine week to look for the zodiacal light if you live in the northern latitudes, now that the evening sky is moonless and the ecliptic tilts high upward from the west horizon at nightfall. From a clear, clean, dark site, look west at twilight's very end for a vague but huge, tall pyramid of pearly light. It's tilted to the left, aligning along the constellations of the zodiac.

What you're seeing is sunlit interplanetary dust orbiting the Sun near the ecliptic plane. Believe it or not, seen from interstellar distances this would be the solar system's brightest feature after the Sun itself. The "zodiacal lights" of dust around other stars may be a real obstacle to someday seeing their small, terrestrial planets.

Wednesday, February 22

Carnivores emerge from hibernation. After dinnertime at this time of year, four carnivore constellations stand upright in a row from the northeast to south. They're all seen in profile with their noses pointed up and their feet (if any) to the right. These are Ursa Major in the northeast (with the Big Dipper as its brightest part), Leo in the east, Hydra the Sea Serpent in the southeast, and bright Canis Major in the south.

• Algol should be at minimum light, magnitude 3.4 instead of its usual 2.3, for a couple hours centered on 9:39 p.m. EST. It takes several more hours before and after to fade and rebrighten.

Thursday, February 23

• Certain deep-sky objects contain secret surprises within or near them. Get out your telescope and sky atlas for a go at Bob King's eight Hidden Gems in Common Deep-Sky Objects now in evening view.

Canis Major, with Sirius

When Sirius shines high in the south, straight below it by 4° is the binocular star cluster M41, appearing small and compact in this wide-field view. This scene spans almost all of Canis Major.

Friday, February 24

• Sirius blazes high in the south on the meridian by about 8 or 9 p.m. now. Using binoculars, examine the spot 4° south of Sirius (directly below it when on the meridian). Four degrees is somewhat less than the width of a typical binocular's field of view. Can you see a dim little patch of speckly gray haze? That's the open star cluster M41, about 2,200 light-years away. Sirius, by comparison, is only 8.6 light-years away.

Saturday, February 25

• Have you ever seen Canopus, the second-brightest star after Sirius? In one of the many interesting coincidences that devoted skywatchers know about, Canopus lies almost due south of Sirius: by 36°. That's far enough south that it never appears above your horizon unless you're below latitude 37° N (southern Virginia, southern Missouri, central California). And there, you'll need a very flat south horizon. Canopus crosses due south just 21 minutes before Sirius does.

When to look? Canopus is due south when Beta Canis Majoris — Mirzam the Announcer, the star about three finger-widths to the right of Sirius — is at its highest point due south (roughly 8:00 p.m. now, depending on how far east or west you are in your time zone). Look straight down from it then. Mirzam is the brightest star to the right of Sirius in the photo above.

• Tomorrow February 26th, an annular eclipse of the Sun will cross parts of southernmost South America, the South Atlantic, and east-central Africa. A partial eclipse will be seen over much larger areas of South America and Africa. Map and details.

Want to become a better astronomer? Learn your way around the constellations! They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Pocket Sky Atlas, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the new Jumbo Edition for easier reading in the night. Click image for larger view.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or new Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, is the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup Jupiter and Spica in early dawn, late Feb. 2017

As dawn begins to brighten this week, Jupiter and Spica shine over the four-star pattern of Corvus, the Crow.

Mercury is hidden deep in the glare of sunrise.

Venus dazzles in the west-southwest during twilight, then lower in the west after dark. Venus is at its peak brightness, magnitude –4.8, all February. Upper left of it is tiny orange Mars, only 0.4% as bright.

In a telescope Venus is a crescent, thinning and enlarging week by week. It's now about 40 arcseconds from cusp to cusp and 25% sunlit. For the rest of the winter, as Venus swings toward us, it will continue to expand as its phase wanes down to a super-thin crescent.

Venus in a telescope is least glary when viewed in bright twilight. So get your scope on it as soon as you can see it naked-eye, even before sunset.

Mars (magnitude +1.2) is the faint "star" upper left of Venus. They widen from 8° to 10° apart this week. In a telescope Mars is just a tiny fuzzblob 5 arcseconds wide.

Vesta, the brightest asteroid, is visible in binoculars at magnitude 6.8 as it moves through Gemini near Pollux and Castor. Article and finder chart.

Jupiter with Red Spot on Jan. 24, 2017

Jupiter on January 24th, imaged by Christopher Go. South is up. Upper left of the Great Red Spot is small, pale-orange Oval BA.

Jupiter (magnitude –2.3, in Virgo) rises around 9 or 10 p.m. and glares highest in the south in the hours before dawn. Spica dangles not quite 4° lower right of it after they rise, more directly below it in the early-morning hours, and lower left of it in early dawn as shown above. Jupiter is creamy white; Spica is an icier shade of white with a trace of blue (once it's fairly high).

In a telescope Jupiter is 41 arcseconds across its equator, on its way to 44 arcseconds in the weeks around its April 7th opposition.

Saturn (magnitude +0.5, on the Ophiuchus-Sagittarius border) rises in the early morning hours and glows in the southeast before and during dawn. Redder Antares, magnitude +1.0, twinkles 17° to Saturn's right.

Uranus (magnitude 5.9, in Pisces) is still in view in the southwest right after dark, in the background of Mars. The two planets will pass 0.6° from each other on the evening of February 26th. Finder chart showing Uranus among its background stars (without Mars).

Neptune is lost in the glow of sunset.

Jupiter's Great Red Spot, 2003 - 2016

Jupiter's Great Red Spot from 2003 to 2016 (starting from the top), showing its changing color and surroundings. Damian Peach assembled this composite from his consistent images taken across the years. Its brick-red color continues in 2017. North is up.


All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time (EST) is Universal Time (UT, UTC, or GMT) minus 5 hours.


"This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours."
— Neil deGrasse Tyson, 2014

"Objective reality exists. Facts are often determinable. Science and reason are no political conspiracy; they are how we discover objective reality. Civilization's survival depends on our ability, and willingness, to do this."
— Alan MacRobert, your Sky at a Glance editor

"Facts are stubborn things."
— John Adams, 1770

March For Science on April 22nd, to “champion publicly funded and publicly communicated science as a pillar of human freedom and prosperity.”


The post This Week’s Sky at a Glance, February 17 – 25 appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Scientists Find Organics on Ceres

Thu, 02/16/2017 - 11:05

The Dawn spacecraft has detected organic compounds on the dwarf planet Ceres.

organic material on Ceres

These Dawn spacecraft data show a region around the crater Ernutet on Ceres where scientists have discovered concentrations of organic material (labeled “a” through “d,” two more in this area not shown). The color coding shows the strength of the organics spectral absorption band, with warmer colors indicating the highest concentrations.
NASA / JPL-Caltech / UCLA / ASI / INAF / MPS / DLR / IDA

Reporting in the February 17th Science, Maria Cristina De Sanctis (INAF Institute for Space Astrophysics and Planetology, Italy) and other members of NASA’s Dawn mission have found a big patch of organic compounds high in the northern hemisphere of the dwarf planet Ceres. Ceres is the largest member of the asteroid belt, and the Dawn spacecraft has been exploring it since 2015.

Organics are not surprising in of themselves. Scientists have found them in meteorites (many of which come from asteroids), and we’ve also seen hints of them on the main-belt asteroids 24 Themis and 65 Cybele. But the signal Dawn picked up is much clearer than the ones from those other asteroids.

The organics drape over the southwest floor and rim of the 50-km-wide crater Ernutet, with a few blobs nearby. However, the compounds don’t look to be connected to the crater itself; they're spread across about 1000 km2. Dawn also detected at least one more, much smaller deposit in Inamahari Crater, about 400 km from Ernutet.

Unfortunately, the scientists couldn’t actually tell what the stuff is, just that it looks like aliphatic organic material. Aliphatic and aromatic are two types of compounds. Aromatic organics have molecular rings of carbon atoms and are fairly “processed,” chemically speaking; aliphatic compounds instead generally have straight chains of carbon atoms and have been less affected by heat and radiation.

There are two reasons the result is interesting. One, Ceres also has tons of water ice, plus carbonates and salts. The addition of organic material makes the dwarf planet a promising environment for prebiotic chemistry.

Two, the organics don’t seem to have been delivered by impacts — no clear cause-and-effect with particular craters, plus a hit probably would have distributed the stuff in diluted form along with other debris. Not to mention there’s other, clearly native material mixed in. Instead, the organics likely come from Ceres itself. Perhaps they’ve been brought up from below by some process, although how remains an open question. Scientists also recently suggested the little world might have a history of ice volcanoes, so maybe it’s more active than we suspected.


Read more about the result in the Southwest Research Institute’s press release. You'll find an in-depth recap of Dawn's discoveries in our December 2016 issue.


Reference: M. C. De Sanctis et al. “Localized aliphatic organic material on the surface of Ceres.” Science. February 17, 2017.


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Categories: Astronomy Headlines

NASA Narrows Down Mars 2020 Rover Landing Sites

Thu, 02/16/2017 - 10:31

Three possible landing sites are now in the running for NASA's Mars 2020 rover.

NE Syrtis Major

A huge inactive shield volcano in NE Syrtis Major.
NASA / JPL-Caltech / University of Arizona

And then there were three. Researchers participating in a workshop held early this month in Monrovia, California, narrowed down the potential landing sites for the Mars 2020 rover to three locations: Columbia Hills, Jezero Crater, and Northeast Syrtis.

The sites selected include regions where water may have flowed and, just possibly, microbial Martian life might once have flourished. The selection process whittled down the three remaining contenders from eight earlier selections.

"The primary scientific factors that drive site selection for the Mars 2020 rover are evidence for an ancient environment with high habitability potential, biosignature preservation potential, and geologic diversity," says Ken Williford (NASA-JPL). "Scientists are particularly interested in landing sites where spectroscopic data from orbit indicate the presence of water-containing minerals in association with these ancient habitable environments."

NASA landing sites

NASA's past landing sites on Mars (yellow) versus the three proposed landing sites (red) for the Mars 2020 rover.
NASA / JPL, with modifications by Dave Dickinson

Here's a brief rundown of the finalists:

Columbia Hills: Mineral springs once came to the surface here in warmer times. If the Columbia Hills region sounds familiar, that's because NASA's Spirit rover explored the region until it finally fell silent in 2010. Spirit's discovery of ancient hot springs in Columbia Hills came as a surprise, and researchers now suspect that a shallow lake once filled the 100-mile (160-kilometer) wide Gusev Crater. If Columbia Hills site is selected, we just might see another first, when the Mars 2020 rover rolls up to the now derelict Spirit rover.

Columbia Hills

Columbia Hills as seen from NASA's Spirit rover.
NASA / JPL-Caltech / Cornell

Jezero Crater: A more daring and remote choice compared to previous NASA landings, Jezero Crater may have flooded and drained at least twice via now-dried-up river channels, which once carried water and clay minerals. Microbial life might have made a home in the crater 3.5 billion years ago.

A false color view of Jezero Crater, showing sediments that have undergone alteration due to chemical interaction with water. NASA/JPL-Caltech/MSSS/JHU-APL

A false color view of Jezero Crater, showing sediments that have undergone alteration due to chemical interaction with water.

Northeast Syrtis: Located near Columbia Hills, volcanic activity may have provided a warm niche for life to flourish here in the early days of Mars. Today, the layered terrain holds a rich record of diverse activity and interactions between minerals and water. It's a place where the chemical reactions leading to life could conceivably have taken hold.

Mars Reconnaissance Orbiter on the Hunt

Analysis of the candidate sites comes courtesy of NASA's Mars Reconnaissance Orbiter (MRO), in orbit around the Red Planet since 2006. With its 0.5-meter aperture HiRISE camera, MRO gives NASA the equivalent of spy satellite resolution from low orbit. The spacecraft has been circling Mars long enough to see changes in sites over the past decade.

“Whether it is looking at the surface, the subsurface, or the atmosphere of the planet, MRO has viewed Mars from orbit with unprecedented spatial resolution, and that produces huge volumes of data,” says MRO project scientist Rich Zurek (JPL-MRO) in a recent press release. “These data are a treasure trove for the whole Mars scientific community to study as we seek to answer a broad range of questions about the evolving habitability, geology, and climate of Mars.”

MRO will have passed along an amazing 300 terabits of information this year, more than every other interplanetary mission combined. MRO has mapped 99% of the surface of Mars down to a resolution of 25 meters or better, including high-resolution swaths over selected sites down to better than a meter resolution. Data collected from MRO will also be incorporated during eventual site selection for crewed missions to Mars in the 2030s.

Mars 2020 versus Curiosity

The Mars 2020 rover resembles Curiosity on the exterior, and like its younger sibling, the Mars 2020 rover will land via sky crane and sport a plutonium-fueled nuclear Radioisotope Thermoelectric Generator (RTG). However, the Mars 2020 rover will use a range trigger during the Entry, Descent and Landing (EDL) phase, which will allow the lander to decide when to open the parachute, reducing the size of the landing ellipse.

Also unlike Curiosity, the Mars 2020 science packages will directly target the question of whether life ever existed on Mars. Moreover, Mars 2020 rover will carry 40 empty tubes for rock cores, with the aim of collecting a cache of surface material for a possible automated sample return mission in the future.

"We can choose a final landing site as late as one year prior to launch," says Williford. "But our goal is to have site selection finalized by two years prior to launch."

Mars 2020 will launch on an Atlas 5 rocket in July 2020 from Cape Canaveral. It should arrive at Mars in early 2021.

If all goes as planned, humanity will really start to invade Mars in the next two launch windows. Only one mission, the European Space Agency (ESA) ExoMars Trace Gas Orbiter and ill-fated Schiaparelli Lander made the trip to Mars in 2016. With Mars launch windows coming around about every 26 months, the next one will arrive in 2018. Watch for NASA's Mars InSight and possibly SpaceX's Red Dragon lander to make the trip then. All four potential landing sites for Mars InSight are within a landing ellipse in Elysium Planitia.

The 2020 mission roll call is far larger, and should include the Mars 2020 rover (it'll have a proper name like every other NASA rover by then), the United Arab Emirates' Mars Hope orbiter, a possible rover fielded by China, ESA's ExoMars rover, and India's second Mars mission.

Get ready as Mars exploration kicks into high gear.

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Categories: Astronomy Headlines