Universe Today

March 15, 2009December 24, 2015 by Anne Minard

Discovery Launch: Sixth Attempt a Charm?

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With just over four hours to go before launch, NASA is 80 percent optimistic that tonight’s Discovery launch will be a go — with the weather holding the only foreseeable wild card. Launch time is 7:43 p.m. local time (EDT) from the Cape Canaveral Air Force Station.

Unfortunately for east coast skywatchers, a storm system that’s been dumping rain all weekend will obstruct a view of the launch that would otherwise be a beauty, as the shuttle will cruise northeast over the ocean nearly parallel to the shore. Without the clouds, the launch would have been visible as far west as the Appalachian Mountains, and as far north as the southern tip of Nova Scotia.

But Florida’s weather is looking promising, partly cloudy (and 80 degrees at the time of this post) with an 80 percent chance of cooperating with the launch.

7:20 p.m. (EDT) update: With less than a half hour to go, daylight is fading under clear skies in Florida. Earlier, the weather forecast improved from 80 percent to 100 percent favorable for launch. NASA is reporting no problems.

The Discovery crew members are set to fly a new truss segment to the International Space Station and install the final set of power-generating solar arrays, boosting the station’s power capacity and paving the way for doubling the size of the ISS crew from three to six.

The Discovery crew has been bouncing between NASA’s Kennedy Space Center, in Florida, and the Johnson Space Center in Houston since late January; the first launch attempt was scheduled for early February. But four times, managers rescheduled the launch based on their concern following a hydrogen control valve malfunction on the shuttle Endeavour last fall. They wanted to rule out any similar glitches on Discovery.

Things were looking good for the fifth attempt on Wednesday — when skies would have been clear across much of the east coast — but a leak during refueling sent up another red flag.

Understandably, this morning’s fueling was a bit tense. But for three hours beginning at 10:20 EDT, nearly 500,000 gallons of chilled liquid oxygen and hydrogen propellants flowed into Discovery’s external tank without incident.

Two irregularities have been reported so far this afternoon: a bat was found clinging to Discovery’s external tank, and Launch Director Mike Leinbach sent a “red team” to launch pad 39A to manually correct a valve issue that caused a drop in helium pressure.

Neither issue is expected to interfere with launch.

Stay tuned for updates, either to this post or a new one.

LEAD IMAGE CAPTION: NASA’s Discovery shuttle pictured under a full moon on Wednesday, when its fifth launch attempt was scrapped. Tonight marks the sixth. NASA/Bill Ingalls

Source: NASA

March 15, 2009December 24, 2015 by Tammy Plotner

Journey Inside M104

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Almost every amateur astronomer is familiar with the Sombrero Galaxy (also known as M104 or NGC 4594) – an unbarred spiral galaxy in the constellation Virgo. We’ve seen it in both small and large telescopes, picked up its ghostly signature in binoculars and dreamed over its structure in photographs. Now, for the first time ever, Jukka Metsavainio is giving us the opportunity to visualize what it might be like to approach this amazing galaxy from space and see it in dimension. Step inside and let’s learn.

Like all our our “stereo” image produced for UT by Jukka Metsavainio, two versions are presented here. The one above is parallel vision – where you relax your eyes and when you are a certain distance from the monitor screen the two images will merge into one to produce a 3D version. The second – which appears below – is crossed vision. This is for those who have better success crossing their eyes to form a third, central image where the dimensional effect occurs. Jukka’s visualizations of what M104 would look like if we were able to see it in dimension comes from studying the object, photographing it, knowing the field star distances and the different wavelengths of light. Are you ready to “cross” the boundary? Then let’s rock…

Discovered by Pierre Mechain in 1781 and added by Charles Messier’s own hand to his personal notes on May 11, 1781, Messier Object 104 wasn’t officially added to the official catalog of Messier objects until 1921 by Camille Flammarion. Although Messier had already ended his studies, he hadn’t quite ended his fascination with the sky and when Pierre discovered this amazing galaxy, he confirmed his observation by adding his description of a “very faint nebula” to the records. On May 9, 1784 – almost three years later to the date – Sir William Herschel independently recovered the galaxy and whose notes state: “Extended [elongated]. Very bright toward the middle. 5 or 6′ long.”

By 1828, John Herschel was seeing things much differently: “There is a faint diffused oval light all about it, and I am almost positive that there is a dark interval or stratum separating the nucleus and general mass of the nebula from the light above (s of) it. Surely no illusion.” Then Emil Dreyer in 1877: “Remarkable, very bright, very large, extremely extended toward position angle 92 deg, very suddenly much brighter toward the middle where there is a nucleus.” And the results of Curtis from the same year “A remarkable, slightly curved, clear-cut dark lane runs along the entire length to the south of the nucleus; probably the finest known example of this phenomenon. There are very slight traces of spiral whorls.” But it was 1912 and Vesto M. Slipher at Lowell Observatory who was about to make the most amazing discovery of all…

During 1910, Slipher (and later Carl Wirtz) was the first to use a spectroscope to observe the radial velocities of galaxies. What Vesto noticed was that M104 appeared to be cruising away from Earth at 700 miles per second. Such an tremendous speed was an important clue that the Sombrero was really another galaxy, and that the universe was expanding in all directions – but they didn’t know that at the time. At home (within our Milky Way galaxy) noted redshifts almost always correspond to the line of sight velocities associated with the objects being observed. These observations of redshifts and blueshifts have allowed science to measure velocities by a method first designed in 1868 by British astronomer William Huggins. Redshift is also an important tool to measure the velocity of gas of interstellar clouds, the rotation of galaxies, and the actions of accretion around neutron stars and black holes.

What we know now is there’s a supermassive black hole at the center of the Sombrero… one of the most massive black holes measured in any nearby galaxies. According the the findings by a research group led by John Kormendy and using spectroscopy data from both the CFHT and the Hubble Space Telescope, the group showed that the speed of rotation of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times the mass of the Sun was present at the core. No wonder the eye is drawn there! The nucleus is also a strong source of synchrotron emission – produced when high velocity electrons oscillate as they pass through regions with strong magnetic fields. Although we can’t see radio waves, the low ionization nuclear emission region (LINER) at M104’s heart may be the energy source that weakly ionizes the gas in the Sombrero Galaxy.

And what of the dark dust ring? It’s cold atomic hydrogen gas. According to infrared spectroscopic studies, it’s the primary site for star formation and not the amazing nucleus. “The brightest infrared sources in the galaxy are the nucleus and the dust ring. The spectral energy distribution of the AGN demonstrates that, while the environment around the AGN is a prominent source of mid-infrared emission, it is a relatively weak source of far-infrared emission, as had been inferred for AGNs in previous research.” Says George Bendo, “The weak nuclear 160 um emission and the negligible polycyclic aromatic hydrocarbon emission from the nucleus also implies that the nucleus is a site of only weak star formation activity and the nucleus contains relatively little cool interstellar gas needed to fuel such activity. We propose that this galaxy may be representative of a subset of low-ionization nuclear emission region galaxies that are in a quiescent AGN phase because of the lack of gas needed to fuel circumnuclear star formation and Seyfert-like AGN activity.”

Take the time to check out this beautiful galaxy yourself. You’ll find it eleven degrees west of Spica….

March 13, 2009December 24, 2015 by Anne Minard

Earth Cyclones, Venus Vortices Have Much in Common

Scientists have spotted an S-shaped feature in the center of the vortices on Venus that looks familiar — because they’ve seen it in tropical cyclones on Earth.

Researchers from the United States and Europe spotted the feature using NASA’s Pioneer Venus Orbiter and The European Space Agency’s Venus Express. Their new discovery confirms that massive, swirling wind patterns have much in common where they have been found — on Venus, Saturn and Earth.

At cloud top level, Venus’ entire atmosphere circles the planet in just about four Earth days, much faster than the solid planet does. Despite this “superrotation,” some dynamical and morphological similarities exist between the vortex organization in the atmospheres of Venus’s northern and southern hemispheres and tropical cyclones and hurricanes on Earth.

Organization of the Venus atmospheric circulation into two circumpolar vortices, one centered on each pole, was first deduced more than 30 years ago from Mariner 10 ultraviolet images. The S-shaped feature in the center of the vortices on Venus was first detected by the Pioneer Venus Orbiter near the northern pole and recently by Venus Express orbiter around the southern pole. It is also known to occur in Earth’s tropical cyclones.

Using an idealized nonlinear and nondivergent barotropic model, lead author Sanjay S. Limaye, of the University of Wisconsin-Madison, and his colleagues are proposing that these S-shaped features are the manifestations of barotropic instability. The feature can be simulated with a barotropic model and, like in the vortices on Venus and in tropical cyclones, it is found to be transient.

Another similarity between the observed features in the vortex circulations of Venus and in terrestrial hurricanes is the presence of transverse waves extending radially outward from the vortex centres. The lack of observations of such features in Earth’s polar vortices is suggestive that the dynamics of the Venus polar vortices may have more in common with hurricanes than their more direct terrestrial counterparts.

Given the challenges in measuring the deep circulation of Venus’s atmosphere, the authors expect that the morphological similarities between vortices on Earth and Venus might help scientists better understand atmospheric superrotation on Venus and guide future observations.

IMAGE CAPTIONS: 1. The ‘eye of the hurricane’ on Venus, taken by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express. The yellow dot represents the south pole. Credit: ESA 2. An infrared satellite image of Hurricane Howard [1998], showing an S-shaped pattern in the low (warm) clouds in the tropical cyclone’s eye. Credit: Sanjay S. Limaye.

Source: Geophysical Research Letters

March 13, 2009December 24, 2015 by Nancy Atkinson

Google Earth Now ‘Live From Mars’

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Google Earth announced a big update today of its Mars features, including a chance to see a continuous stream of new, high resolution satellite imagery just hours after NASA receives them. Called “Live from Mars,” this section features imagery from NASA’s THEMIS camera on board the Mars Odyssey spacecraft, and the HiRISE Camera from the Mars Reconnaissance Orbiter. You can become one of the very first people to lay eyes on images taken just days or even hours ago. You can also see live satellite orbital tracks, or check out where these cameras plan to image next.

But wait! There’s more! Users can also travel back in time to see the Red Planet through the eyes of the pioneers of Mars science in the ‘Historical Maps’ layer by exploring antique maps by astronomers Giovanni Schiaparelli, Percival Lowell, and others. But also, if you don’t know exactly where to start with your Mars exploration, there are guided tours of Mars narrated by Ira Flatow of Public Radio’s Science Friday and Bill Nye the Science Guy, allowing you to enjoy the PB&J (passion, beauty and joy) of the Red Planet through their eyes.

So how do you enjoy these new features? Open Google Earth, and after selecting ‘Mars’ from the toolbar in Google Earth, users fly to a 3D view of the Red Planet, complete with informational layers, imagery, and terrain. The tools for navigation and exploration on Mars are identical to those on Earth – zoom in and out, change the camera view, or spin the entire planet with a click of the mouse.

Historical maps in Google Mars. Credit: Google.

Just as in the original version of Mars in Google Earth, users can read geo-located articles from Hartmann’s “A Traveler’s Guide to Mars” about the solar system’s largest canyon, Valles Marineris, its tallest volcano, Olympus Mons, the infamous ‘Face on Mars’, and many other famous Martian locations. Users can also follow the paths of Mars rovers and view hi-resolution panoramic photos of the Mars surface.

Google’s Communication and Public Affairs officer Aaron Stein noted the “Live From Mars” imagery is the most current available from the THEMIS camera. ” Our live imagery is the most current available imagery from THEMIS,” he said. “It’s not unusual for NASA to save up and download one or two days of images at a time, so downloads do not always occur within hours of image acquisition. Despite this, Live from Mars is orders of magnitude more “live” than the typical NASA public data release process, which for Mars imagery typically takes many months.”

Enjoy — It’s fun, it’s free, and a great way to lose yourself for a few hours!

Source: Google Earth

March 13, 2009December 24, 2015 by Fraser Cain

Shield Volcanoes

Color mosaic of Mars' greatest mountain, Olympus Mons, viewed from orbit. Credit NASA/JPL

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Shield volcanoes are large volcanoes with gently sloping sides. In fact, the largest volcanoes on Earth (and even the Solar System) are shield volcanoes. They form when lava flows of low viscosity build up over long periods of time, creating volcanoes with huge internal volume. The best known shield volcanoes are ones that make up the Big Island of Hawaii: Mauna Loa and Mauna Kea.

The common feature with shield volcanoes is that they’re built up slowly over time from a very stable central summit vent. Flow after flow pours out of the vent, slides down the slopes of the volcano, and builds up the size. The largest volcanoes, like Mauna Loa and Mauna Kea would have been created from thousands of these flows.

Shield volcanoes can be found around the world. In northern California and Oregon, they can be 5-10 km across and about 500 meters high. But in the Hawaiian Islands, the volcanoes were atop very active vents for millions of years. Mauna Loa projects 4,168 meters above sea level, but if you measure it from the base of the ocean to its top, it measures 8,534 meters. (Mount Everest is 8,848 meters tall).

Volcanic activity is linked to plate tectonics, and the most of the world’s volcanoes are located near plate boundaries where subduction is happening. This is where one plate is passing under another plate, sinking into the Earth’s mantle.

The largest shield volcano in the Solar System is Olympus Mons on Mars. This monster measures 27 km above the surface of Mars, and is 550 km in width. It’s believed that Olympus Mons got so big because Mars lacks plate tectonics. A single volcanic hotspot was able to channel lava for billions of years, building up the volcano to such a great size.

We have written many articles about the Earth for Universe Today. Here’s an article about Olympus Mons, and here’s an article about Mauna Kea and Mauna Loa.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

March 13, 2009December 24, 2015 by Tammy Plotner

Weekend SkyWatcher’s Forecast – March 13-15, 2009

Greetings, fellow SkyWatchers! With the Moon gone from the early evening skies, it’s time for a little sky dancing this weekend. Are you ready for a little old stepping out and a little new? Then waltz this way as we check out some very new star clusters and interesting asterisms! Grab your binoculars and telescopes and I’ll meet you in the back yard….

Friday, March 13, 2009 – Today note the 1886 birth of Albert William Stevens, a daring balloonist who took the Explorer II to an altitude of 72,395 feet. He took the first photo showing Earth’s curvature and the first solar eclipse photo of the Moon’s shadow on Earth. Also, salute the 1855 birth on this date of Percival Lowell, who predicted the existence of Pluto (but Clyde Tombaugh was the one who actually discovered it, on Lowell’s 75th birthday!). Sir Percival was a determined soul who spent his life trying to find proof of life on Mars. He founded Lowell Observatory in 1894, where he studied Mars intensively, drawing the Red Planet covered with canals and oases. As Lowell once said: ‘‘Imagination is as vital to any advance in science as learning and precision are essential for starting points.’’

Tonight we’ll look at a bright collection of stars located less than a handspan west of Procyon. Its name is Collinder 106 (RA 06 37 19 Dec -05 57 55). At a combined magnitude of 4.5, this expansive open cluster can be spotted as a hazy patch with the unaided eye and comes to full resolution with binoculars. It contains only around 14 members, but this widely scattered galactic collection has helped scientists determine size scales and dispersion among groups of its type. Viewed telescopically at low power, the observer will find it rich in background stars and a true delight in a low power, wide field eyepiece. If you’d like a challenge, hop a half degree to the northeast to spot Collinder 111 (RA 06 38 42 Dec -06 54 00). While visually only about one-tenth the apparent size of its larger southwestern neighbor, spare little Collinder 111 also belongs to the same class of open clusters. Who knows what may lurk around these understudied clusters?

Saturday, March 14, 2009 – Before dawn, look for the close appearance of Spica and the Moon to celebrate today’s famous astro births, starting with astronaut Frank Borman (b. 1928), a crew member of Apollo 8, the first manned flight around the Moon. Next, astronaut Eugene Cernan (b. 1934), who floated in space for more than 2 hours during the Gemini 9 mission and piloted Apollo 10. How about Giovanni Schiaparelli (1835), the Italian astronomer who described Mars’s ‘‘canali’’ and named its ‘‘seas’’ and ‘‘continents.’’ Schiaparelli’s comet studies demonstrated that meteoroid swarms existed in the path of cometary orbits, and thus predicted annual meteor showers. He was first to suggest that Mercury and Venus rotate and discovered the asteroid Hesperia. Still not enough? Then wish a happy birthday to Albert Einstein (b.1879), the German–American physicist considered the most brilliant intellect in human history!

For a moment let’s reflect on Einstein’s Cross, proof of his genius. We can’t observe this Pegasus-based gravitational lens right now, but we can try to understand Einstein’s theory of gravity as an effect of the curvature in space–time. For example, if you draw a line around the center of a ball, the line would be straight, eventually coming back to its point of origin. We don’t see the point until we reach it, but we know it’s there. Einstein knew this dimension existed and predicted any object with mass will bend space and time around it, just like our line around the ball. He predicted light would also follow a curved path around an object… such as a distant quasar located behind a closer galaxy!

Tonight’s object is a ‘‘cross’’ astersim of stars. Begin at Procyon and shift about 10 degrees southwest (or 2 degrees south of 18 Monocerotis) to locate this pretty grouping of stars. Yes it’s true. It’s just an unknown, undocumented, and unnamed asterism, but how fitting to honor all these famous astro figures and a brilliant man who once said: ‘‘The fairest thing in life we can experience is the mysterious. It… stands at the cradle of true art and true science.’’

Now let’s go for a a challenging study. Larger telescopes should look for diminutive Bochum 2 less than half a degree northeast of ‘‘Einstein’s Asterism’’ (RA 06 48 50 Dec 00 22 35). At low power, it’s just a tight configuration of stars, but test the limit your telescope and increase magnification. This young open cluster has been studied for internal kinematics, spectroscopic binaries, and its motion in the galaxy, but its most interesting feature is a trapezium system at its heart. After a 4-year study, two of the members were documented as close binary stars with highly eccentric orbits, and one of the members is leaving as a runaway!

For smaller optics, continue another half degree east for NGC 2301 (RA 06 51 48 Dec -00 28 00). Even telescopes as small as Lacaille’s can see this bright, 2,500 light-year-distant open cluster. Studied for its variable stars, NGC 2301 is also on many binocular deep-sky observing lists!

Sunday, March 15, 2009 – Today marks the 1713 birth of Abbe Nicolas Louis de Lacaille, the French astronomer who named 15 of the 88 constellations. Using only a half-inch refractor, Lacaille made 26 new discoveries and charted 9,776 stars, creating the first southern star catalog. Sharing the date is William Rutter Dawes (b. 1799). ‘‘Eagle-eyed’’ Dawes made exhaustive measurements of binary stars, discovered Saturn’s inner Crepe Ring, and accurately mapped Mars. Dawes also devised the elegantly simple formula (Dawe’s Limit) of dividing the number 11 by the aperture in centimeters to give the arcseconds of resolution required to split a binary star.

Thankfully, somebody was watching the sky at 5:30 p.m. on this date in 1806, because the observed fall of a pristine 6-kilogram chondrite meteor made an indisputable case that chondrites carried carbon-based organic chemicals. Perhaps it was from one of the Corona Australid meteors whose shower peak is tonight after midnight? The fall rate is about 5–7 per hour, and best for our friends in the southern hemisphere!

Tonight let’s return to the Einstein’s Asterism and drop 15 degrees due southeast to study open cluster NGC 2360 (RA 07 17 42 Dec -15 38 00). At a distance of 4,600 light-years, magnificent NGC 2360 contains around 40 members, 7 of which are red giants. You have Caroline Herschel to thank for this lovely cluster… and her birthday is tomorrow!

Now, return to our Einstein’s Asterism and head slightly more than half a degree west to study scattered open cluster Dolidze 25 (RA 06 45 06 Dec -00 18 00). This low power, telescopic only, galactic cluster is a worthy study for those who seek the unusual. Located at the outer edges of our own galaxy, Dolidze 25 may very well be the product of the merger of the Milky Way and the Canis Major Dwarf galaxy. Extremely rich in oxygen and significantly deficient in metals, this huge starforming region contains young stars, pre-main sequence stars, and Delta Scuti types. With its thin veil of nebula, Do25 should prove to be challenging and quite to your liking! Hop another half degree west, and then slightly south for Dolidze 23 (RA 06 43 12 Dec -00 00 00). This telescope-only cluster reveals around a dozen easily resolvable stars at low power. Dolidze 23’s two brighter members are finderscope visible. Locate the cluster at low power, and place it at the south edge of the field of view. Turn off your drive units and allow the field to cruise by naturally as you observe. This allows Dolidze 25 to drift across your line of sight, a technique that often improves your ability to spot fine detail in fainter objects.

Celestial scenery alert on Tuesday, March 17! A few hours before dawn, the Moon and mighty Antares will be nearly touching, separated by only a fraction (0.2) of a degree. For some, this could be a wonderful occultation event, so be sure to check maps and resources! Although the occultation path is limited, even more so is the graze path, just a few kilometers wide. For these lucky viewers, brilliant red Antares may flash in and out of view several times as it moves slowly along behind the lunar mountains.

Until next week, dreams really do come true when you keep on reaching for the stars!

This week’s awesome photos are: Sir Percival Lowell (historical image), Collinder 106 (credit – Palomar Observatory, courtesy of Caltech), Einstein’s Cross (credit – HST/NASA), “Einstein’s Asterism’’ (Credit – Palomar Observatory, courtesy of Caltech), Bochum 2, NGC 2301, Dolidize 25 and NGC 2360 (credit – Palomar Observatory, courtesy of Caltech). Thank you so much!

March 13, 2009December 24, 2015 by Nancy Atkinson

Herschel and Planck Launch Delayed

Guyana Space Center Credits: ESA - S. Corvaja

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The launch of the Herschel and Planck spacecraft has been delayed from the original launch date of April 16. Right now, officials from the European Space Agency and Arianspace say the liftoff date will be delayed by a few weeks in order to carry out additional checks on the ground segment of the Herschel and Planck programs. Recent software updates for spacecraft operation procedures need to be validated. A new launch date will be announced at the end of March, but officials are hoping for time frame around April 29.

Launch configuration for the Herschel and Planck spacecraft. Credit: ESA

Planck, ESA’s microwave observatory that will study the relic radiation of the Big Bang, while the Herschel missions will study the formation of stars and galaxies. The two will be launched together on an Arian 5 rocket.

Planck is designed to image the anisotropies of the Cosmic Background Radiation Field over the whole sky, with unprecedented sensitivity and angular resolution. It will provide a major source of information relevant to several cosmological and astrophysical issues, such as testing theories of the early universe and the origin of cosmic structure.

The Herschel Space Observatory (formerly called Far Infrared and Sub-millimetre Telescope or FIRST) has the largest single mirror ever built for a space telescope. At 3.5-meters in diameter the mirror will collect long-wavelength radiation from some of the coldest and most distant objects in the Universe. In addition, Herschel will be the only space observatory to cover a spectral range from the far infrared to sub-millimeter.
During the delay, preparation of the two spacecraft for launch continues as planned at Europe’s Spaceport in Kourou, French Guiana.

Source: ESA

March 13, 2009December 24, 2015 by Ian O'Neill

Looking For Extraterrestrials Looking At Us

If there are habitable planets out there, where do we look?

[/caption]The cosmos is a very big place, how do you begin the search for exoplanets orbiting other stars? Astronomers have a few tricks up their sleeves to work out how to spot these tiny specks of distant alien worlds. Astronomers can look for the gravitational “wobble” of a star as a massive exoplanet tugs on its parent star during orbit, or more commonly, they look for the slight dimming of star light as the exoplanet passes in front of the star. In fact, the Kepler space telescope is going to peer into space, surveying 100,000 stars to do just this; not looking for large gas giants, but detecting rocky bodies that resemble large Earths with the unparalleled precision.

OK, so we have a means of finding these habitable worlds, how can we use this information to widen our search for extraterrestrial intelligence? Researchers in Israel have asked that same question, and arrived at a very logical answer. If we are to communicate with these advanced beings, perhaps we should make sure they can see us first…

The concept is simple enough. Find a star with an Earth-like transiting exoplanet (we will hopefully have a few super-Earth targets over the next three years with Kepler), aim a radio transmitter at the star and send a “Hello world!” message to the possible alien civilization living on the exoplanet. All going well (or not, depending on whether these extraterrestrials are actually friendly), we’ll get a reply from said star system in a few decades with a message saying something like “Hello world to you too!”. It would be a momentous day for interstellar communications and it would answer the one question that bugs astronomers everywhere: Are we alone in the cosmos?

So far so good, until interstellar travel becomes a reality, mankind and our new chatty alien neighbours can play a very long game of radio tag, learning more about each other as the years/decades/centuries go on (depending on how distant the extraterrestrial civilization is in the first place). But there’s a problem with this plan. What if our ET neighbours aren’t looking in our direction? What if the Sun looks like ‘just another’ star amongst the other 10¹⁰ Sun-like stars hanging out in the Milky Way? We can transmit to our hearts content, but they may never see us.

Shmuel Nussinov at Tel Aviv University in Israel asked these same questions and actually makes the search for extraterrestrial intelligence a little bit easier. With the assumption that a sufficiently advanced alien race is surveying the skies, also looking out for exoplanets orbiting other stars, they may be using the same transit method that we use to detect exoplanets. Therefore, it only seems reasonable that ET will only be able to detect Earth if we pass in front of the Sun, thus dimming it slightly for our alien neighbours to see us. If this is the case, it seems highly unlikely that any alien race will detect our existence unless they are located along a narrow angle along the ecliptic plane of our Solar System. So, if we want to open up some alien banter, we should perhaps send signals to Earth-like exoplanets spotted along the ecliptic.

Although the Earth only passes across the solar disk for 13 hours every year (as viewed by a distant observer), our star will appear to dim slightly, allowing ET to see us. Factor in the various transits of the inner Solar System planets, and our observers will see there are a few possibly habitable rocky “exoplanets” for them to transmit to. If we are already transmitting, communications can be exchanged.

What a good idea…

Source: arXiv blog

March 12, 2009December 24, 2015 by Anne Minard

New Horizons Spots Neptune’s Moon Triton

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New Horizons got a great shot of Neptune’s moon Triton last fall, as it was trucking toward Pluto and the Kuiper Belt.

The mission was 2.33 billion miles (3.75 billion kilometers) from Neptune on Oct. 16, when its Long Range Reconnaissance Imager (LORRI) locked onto the planet and snapped away. The craft was following a programmed sequence of commands as part of its annual checkout. NASA released the image Thursday afternoon.

Mission scientists say the shot was good practice for imaging Pluto, which New Horizons will do in 2015. Neptune’s moon Triton and Pluto — the former planet retitled in 2006 as the ambassador to the Kuiper Belt — have much in common.

“Among the objects visited by spacecraft so far, Triton is by far the best analog of Pluto,” said New Horizons Principal Investigator Alan Stern.

Triton is only slightly larger than Pluto, boasting a 1,700-mile (2,700-kilometers) diameter compared to Pluto’s 1,500-mile (2,400-kilometer) girth. Both objects have atmospheres primarily composed of nitrogen gas with a surface pressure only 1/70,000th of Earth’s, and comparably cold surface temperatures. Temperatures average -390 degrees F (-199 degrees C) on Triton and -370 degrees F (-188 degrees C) on Pluto.

Triton is widely believed to have once been a member of the Kuiper Belt that was captured into orbit around Neptune, probably during a collision early in the solar system’s history. Pluto was the first Kuiper Belt object to be discovered.

Furthermore, “We wanted to test LORRI’s ability to measure a faint object near a much brighter one using a special tracking mode,” said New Horizons Project Scientist Hal Weaver, of Johns Hopkins University, “and the Neptune-Triton pair perfectly fit the bill.”

LORRI was operated in 4-by-4 format (the original pixels are binned in groups of 16), and the spacecraft was put into a special tracking mode to allow for longer exposure times to maximize its sensitivity.

Mission scientists also wanted to measure Triton itself, to follow up on observations made by the Voyager 2 spacecraft during its flyby of Neptune in 1989. Those images revealed evidence of cryovolcanic activity and cantaloupe-like terrain. New Horizons can observe Neptune and Triton at solar phase angles (the Sun-object-spacecraft angle) that are not possible to achieve from Earth-based facilities, yielding new insight into the properties of Titan’s surface and Neptune’s atmosphere.

New Horizons is currently in electronic hibernation, 1.2 billion miles (1.93 billion kilometers) from home, speeding away from the Sun at 38,520 miles (61,991 kilometers) per hour. LORRI will continue to observe the Neptune-Triton pair during annual checkouts until the Pluto encounter in 2015.

LEAD IMAGE CAPTION: The top frame is a composite, full-frame (0.29° by 0.29°) LORRI image of Neptune taken Oct. 16, 2008, using an exposure time of 10 seconds and 4-by-4 pixel re-binning to achieve its highest possible sensitivity. The bottom frame is a twice-magnified view that more clearly shows the detection of Triton, Neptune’s largest moon. Neptune is the brightest object in the field and is saturated (on purpose) in this long exposure. Triton, which is about 16 arcsec east (celestial north is up, east is to the left) of Neptune, is approximately 180 times fainter. All the other objects in the image are background field stars. The dark “tails” on the brightest objects are artifacts of the LORRI charge-coupled device (CCD); the effect is small but easily seen in this logarithmic intensity stretch. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

Source: NASA

March 12, 2009December 24, 2015 by Nancy Atkinson

Dawn Spacecraft on Target for Vesta Following Gravity Assist

This image was taken near the point of closest approach to Mars on Feb. 17, 2009, during Dawn's gravity assist flyby. Image credit: NASA/JPL/MPS/DLR/IDA, and the Dawn Flight Team

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Recently, the Dawn spacecraft – on its circuitous route to the asteroid belt — used the gravity of Mars to provide a little ‘kick’ to the spacecraft’s velocity. Universe Today finally had the chance to catch up with the team from the Dawn mission following this maneuver to find out how things went, and how the spacecraft is doing following the gravity assist operations. “The gravity assist accomplished exactly what we needed to get on course for Vesta,” Dawn Chief Engineer Marc Rayman told UT. “In addition to the gravity assist, we decided to undertake some bonus instrument calibrations, taking advantage of flying by such a well-studied planet. In doing so, we obtained some performance data on some of our instruments.” The image seen here of Mars’ surface is one of the results of those calibrations.

Dawn will be visiting two different asteroids, Vesta and Ceres. Because of its distinctive ion engine, the spacecraft will be able to enter orbit around Vesta in August of 2011, remain there until May of 2012, then leave orbit and head to Ceres, arriving in February of 2015.

The thrusters work by using an electrical charge to accelerate ions from xenon fuel to a speed 10 times that of chemical engines. But what does this mean for a gravity assist – is there any difference between an ion engine versus and a chemical thruster in a gravity assist?

“In most ways, there is no difference,” said Rayman. “We used the ion thruster to get on course for the gravity assist, but the spacecraft coasted for most of the 4.5 months before it reached Mars. When we had to refine the trajectory, we used the ion thruster because it is so much more efficient than conventional propulsion. Moreover, because the ion propulsion affords so much flexibility in the mission, we did not have to hit as small a ‘window’ at Mars.”

Generally, a gravity assist is used to increase a spacecraft’s velocity and propel it outward in the solar system, much farther away from the Sun than its launch vehicle would have been capable of doing.

Dawn got as close as 549 kilometers (341 miles) to the Red Planet during the Tuesday, Feb. 17, flyby. JPL said that if Dawn had to perform these orbital adjustments on its own, with no Mars gravitational deflection, the spacecraft would have had to fire up its engines and change velocity by more than 9,330 kilometers per hour (5,800 miles per hour).

At maximum thrust, each engine produces a total of 91 millinewtons — about the amount of force involved in holding a single piece of notebook paper in your hand. You would not want to use ion propulsion to get on a freeway: At maximum throttle, it would take Dawn’s system four days to accelerate from 0 to 60 miles per hour.

Using the gravity of Mars was an important part of the Dawn mission that makes going to the asteroid belt possible.

Sources: JPL, email exchange with Marc Rayman