A Trojan Asteroid for Earth

by Paul Gilster on July 29, 2011

Although the asteroid temporarily called 2010 TK7 was discovered late in 2010, we now learn in the latest issue of Nature that this object is our planet’s first known Trojan asteroid. The term refers to objects that orbit around one of the two Lagrangian points L4 and L5 — these are found 60° ahead of and behind the larger body. Trojans come in various sizes. The Saturn system actually has Trojan moons (Telesto and Calypso, which accompany Tethys, and Helene and Polydeuces, which move in orbital configuration with Dione). Jupiter, Neptune, Mars and now the Earth have all been found to have Trojan asteroids associated with them.

As the paper on this work points out, the viewing geometry poses problems for discovering Trojan asteroids moving with our planet, although we have found unusual objects like the ‘horseshoe orbiters’ 2010 SO16 and 3753 Cruithne. What made the current discovery possible was the Wide-field Infrared Survey Explorer (WISE) satellite, which searched large areas of the sky 90º from the Sun with a high level of astrometric precision (2010 SO16 was identified through the same data). Follow-up study with the Canada-France-Hawaii Telescope in 2011 allowed the orbit of 2010 TK7 to be determined, verifying its status as an Earth Trojan.

It’s worth noting that the NEOWISE component of the WISE mission focused on near-Earth objects like asteroids and comets, observing more than 155,000 main belt asteroids and tracking more than 500 NEOs, including 132 that were being seen for the first time. Trojans are still difficult to spot, but 2010 TK7 fell within the parameters of the WISE coverage area:

“These asteroids dwell mostly in the daylight, making them very hard to see,” said Martin Connors of Athabasca University in Canada, lead author of the paper on the discovery. “But we finally found one, because the object has an unusual orbit that takes it farther away from the sun than what is typical for Trojans. WISE was a game-changer, giving us a point of view difficult to have at Earth’s surface.”

As you can see in the image below, 2010 TK7 follows a complex path that moves it sometimes closer and sometimes farther from the Earth, with the asteroid preceding the Earth at all times as both move around the Sun.

Image: The complete path of asteroid 2010 TK7 (green) during the course of one of its 195-year cycles. The asteroid remains in front of the Earth as they both orbit the Sun. The asteroid is the white sphere, the Sun the yellow sphere, and the dark blue dots trace out the Earth’s orbit. Credit: Paul Wiegert, University of Western Ontario, Canada.

Could a Trojan like this become a tempting target for a space mission? The paper notes the problem: 2010 TK7 is in a highly inclined orbit, traveling far above and below the plane of the Earth’s orbit. The delta-v required is 9.4 km/s. This contrasts with values of below 4 km/s for other near-Earth asteroids, making other objects more likely candidates. In any case, we still have much to learn about this Trojan. Its absolute magnitude allows an estimate of 300 meters for its diameter, making it relatively large among the near-Earth asteroid population. It’s presently about 80 million kilometers from the Earth, and we also learn that no spectral or color information is yet available to tell us whether it is unusual in any way that might justify a mission.

The animation below illustrates the orbit of 2010 TK7.

Image: The movie follows Earth as it travels along its orbit (blue dots) around the sun, so Earth remains at the front of our view. The various objects are not drawn to scale. Asteroid 2010 TK7 has an extreme orbit that takes the asteroid far above and below the plane of Earth’s orbit. The motion above and below the plane is referred to as an epicycle. In addition, the asteroid moves within the plane of Earth’s orbit in what is called libration, circling horizontally around its stable point every 395 years. The clock at upper left shows how the orbit changes over time. The asteroid’s orbit is well understood — over the next ten thousand years, 2010 TK7 will not approach Earth any closer than 20 million kilometers (12.4 million miles), which is more than 50 times the distance from Earth to the moon. Credit: Paul Wiegert, University of Western Ontario, Canada.

The paper is Connors et al., “Earth’s Trojan Asteroid,” Nature 475 (28 July 2011), pp. 481–483 (abstract). See also the discoverers’ article Earth’s First Trojan Asteroid: 2010 TK7.

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A Shield from Stellar Eruptions?

by Paul Gilster on July 28, 2011

We don’t know whether life can exist on a planet circling a red dwarf, but as reported in these pages frequently in the last few years, there have been studies showing that liquid water could persist on the surface of such planets despite the fact that they would most likely be tidally locked, with one side always facing their star. So the potential is there, but we also have to account for flare activity and the question of how life might adapt to it. Perhaps there are protective mechanisms that might shield such planets from the worst such eruptions, a possibility now raised by Ofer Cohen (Harvard-Smithsonian Center for Astrophysics).

Cohen and team have recently gone to work on planets of a far different kind — hot Jupiters crowded up in tight orbits around more Sun-like stars — but the work on gas giants is intended to lead on to a close look at red dwarf planets in similar proximity to violent stellar events. Until that study is complete, we can learn from their work on what happens when a coronal mass ejection (CME) hits a nearby planet. A CME pumps billions of tons of electrically charged hot gas into the Solar System, an event that can cause major disruptions to the Earth’s magnetosphere. It was a CME and ensuing geomagnetic storm that blacked out large regions of Quebec back in 1989.

Much tamer phenomena are likewise markers for solar activity, as anyone who has been fortunate enough to experience the Northern or Southern Lights already knows. My first encounter with the Northern Lights was in Iowa back in my college days, when the northern sky one night seemed to mimic a huge open window with gauzy white curtains being blown by the wind. It was an eerie, though not colorful, phenomenon, and I heard at the time that the lights were fairly rare at our comparatively low latitude. Years later in Iceland I would get the Northern Lights in technicolor one late October, a stunning display that had me standing speechless looking out over Reykjavik’s docks at the rippling and ever changing stream of colors.

Cohen’s work on aurorae shows that distant hot Jupiters should experience the same phenomena, though peaking at 100 to 1000 times the brightness of what we see on Earth. When a Coronal Mass Ejection hits a gas giant just a few million miles from its star, the planet would be subject to extreme forces, feeling the concentrated might of the blast. The immediate effect would be a weakening of the planet’s magnetic shield. And as CME particles reaches the planet’s atmosphere, the auroral lights would manifest themselves first as a ring around the equator that would, in the course of six hours, move up and down toward the planetary poles.

Image: This artist’s conception shows a “hot Jupiter” and its two hypothetical moons with a sunlike star in the background. The planet is cloaked in brilliant aurorae triggered by the impact of a coronal mass ejection. Theoretical calculations suggest that those aurorae could be 100-1000 times brighter than Earth’s. Credit: David A. Aguilar (CfA).

Remarkably, the hot Jupiter itself seems relatively well protected by its magnetic field. Cohen’s simulations show that the initial orientation of the planetary magnetosphere (which is elongated into a comet-like tail by the stellar wind) is almost perpendicular to the CME’s direction, with the result that the CME is modified in highly complex ways. But the key finding is that even in such extreme conditions, the planet’s atmosphere can be shielded from erosion. From the paper:

Despite its proximity to the host star, we find that the planet is well shielded from being eroded by the CME, even with a relatively weak intrinsic magnetic field of 0.5 G. We also find that the planetary angular momentum loss associated with a disconnection of part of the planetary tail is negligible compared to the total planetary angular momentum. Our simulation suggests that the planetary magnetosphere can be significantly affected by the CME event, and that the energization of the planetary magnetospheric-ionospheric system might be much higher than in the Earth. It also suggests a transition in the magnetospheric Alfvén wings [wedge-shaped structures of magnetospheric plasma] configuration during the event, as well as a rotation of the whole current system by 90°. However, our simulation cannot provide such detailed information about the planetary properties; investigation of these aspects of the interaction requires a detailed numerical model for the planetary magnetosphere.

So a hot Jupiter gets pummeled by a CME, but the power of its protective mechanism is surprising, and as Cohen points out in this CfA news release, “…even a planet with a magnetic field much weaker than Jupiter’s would stay relatively safe.” How to extend such findings in the direction of stellar activity on red dwarfs and the consequent effect on planets there? We have much to learn, but perhaps this team’s continuing investigation in that direction will clarify whether discovering a planet in a red dwarf’s ‘habitable zone’ really does flag a potential for exoplanetary life.

The paper is Cohen et al., “The Dynamics of Stellar Coronae Harboring Hot-jupiters II. A Space Weather Event on A Hot-jupiter,” accepted by the Astrophysical Journal (preprint).

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Water in the Distant Universe

by Paul Gilster on July 27, 2011

Although I wasn’t able to do any traveling during my recent week off, I did manage to get in some backed up reading, including Iain Banks’ Use of Weapons (2008), the third in his series of novels about the interstellar civilization known as ‘The Culture.’ I’ve developed quite an interest in Banks, whose novels paint a future so finely textured that the memory of it lingers like a flashback to an actual experience, an intuitive, almost mystical sense that I remember having encountered when I first read Cordwainer Smith (Paul Linebarger) many years ago (some of Jay Lake’s short stories also have this effect on me). Thanks to the many Centauri Dreams readers who put me on to Banks’ novels.

Among the events in astrophysics that occurred during my absence, I was most struck by the discovery of vast amounts of water surrounding a black hole more than 12 billion light years away, an indication, in the words of JPL’s Matt Bradford, that “water is pervasive throughout the universe, even at the very earliest times.” This one triggers a more traditional science fictional sense of wonder in a major way, if for no other reason than the sheer scale of the objects involved. The quasar APM 08279+5255 harbors a black hole 20 billion times more massive than the Sun and, according to this NASA news release, produces an amount of energy equal to a thousand trillion suns. That’s 65,000 times the energy output of the entire Milky Way galaxy.

Image: This artist’s concept illustrates a quasar, or feeding black hole, similar to APM 08279+5255, where astronomers discovered huge amounts of water vapor. Gas and dust likely form a torus around the central black hole, with clouds of charged gas above and below. X-rays emerge from the very central region, while thermal infrared radiation is emitted by dust throughout most of the torus. While this figure shows the quasar’s torus approximately edge-on, the torus around APM 08279+5255 is likely positioned face-on from our point of view. Credit: NASA/ESA.

The huge black hole, pulling in surrounding gas and dust and spewing out energy, is what powers up the quasar, an object of a class known to contain the most luminous and most energetic objects in the universe. And what the paper on this work tells us is that the cloud of water vapor associated with this object contains the equivalent of 140 trillion times all the water in the world’s oceans. Studying such phenomena tell us much about the early universe, according to co-author Alberto Bolatto:

“Because the light we are seeing left this quasar more than 12 billion years ago, we are seeing water that was present only some 1.6 billion years after the beginning of the Universe. This discovery pushes the detection of water 1 billion years closer to the Big Bang than any previous find.”

The water vapor is found in a gaseous region that spans hundreds of light years, a cloud whose temperature is minus 53 degrees Celsius, unusually warm in astronomical terms. In fact, the cloud is five times hotter and between 10 and 100 times denser than gases typical to galaxies like the Milky Way. There seems to be enough water vapor — and other molecules, including carbon monoxide — to feed the black hole until it grows to six times its current size, though at this point no one can say how much of the gas will actually wind up being absorbed by it.

While water vapor is present in the Milky Way, it appears in amounts 4000 times less massive than what we find in the quasar, in part because most of the water in our galaxy is frozen into ice. The discovery is owed to work done with the Z-Spec spectrograph at the Caltech Submillimeter Observatory on Mauna Kea, operating in the millimeter wavelengths. And it’s an indication of more to come at these wavelengths, according to Jason Glenn (University of Colorado at Boulder), who is a co-principal investigator on the Z-Spec:

“Breakthroughs are coming fast in millimeter and submillimeter technology, enabling us to study ancient galaxies caught in the act of forming stars and supermassive black holes. The excellent sensitivity of Z-Spec and similar technology will allow astronomers to continue to make important and surprising findings related to distant celestial objects in the early universe, with implications for how our own Milky Way galaxy formed.”

Astronomers including the authors of this study are working on the design for CCAT, a 25-meter telescope destined for Chile’s Atacama desert, which will push yet deeper into the universe at millimeter and submillimeter wavelengths. We can expect CCAT to continue the study of gas content and water vapor in some of the earliest galaxies in the universe. The current paper is Bradford et al., “The Water Vapor Spectrum of APM 08279+5255: X-Ray Heating and Infrared Pumping over Hundreds of Parsecs,” accepted by Astrophysical Journal Letters (preprint).

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A Brief Summer Break

by Paul Gilster on July 18, 2011

It hasn’t escaped my attention that in the past seven years, I’ve taken no more than a couple of days off at a time from writing Centauri Dreams posts. Now that the doldrums of summer are here in the northern hemisphere, it seems a good time to take a somewhat longer break. Not that I’ll stay away if something major happens — if Debra Fischer announces rocky worlds around Centauri B, for example, I’ll be all over the story. But a week off will provide the chance to reflect, recharge, and get in some backed up but necessary reading. I’ll plan to have the next Centauri Dreams post up, then, some time next week, probably by the 27th, and then back to normal.

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Two Relatively Near Brown Dwarfs

by Paul Gilster on July 15, 2011

Two brown dwarfs relatively near to the Sun may be just the first such objects we’ll soon identify with data from the WISE (Wide-field Infrared Survey Explorer) satellite. Ralf-Dieter Scholz (Leibniz-Institut für Astrophysik, Potsdam) and colleagues have gone to work on a search for brown dwarfs with high proper motion, looking for brown dwarfs in the immediate solar neighborhood using not just the preliminary WISE data release but the previous near-infrared (2MASS) and deep optical (SDSS) surveys. The search has already begun to pay off.

The two brown dwarf discoveries — WISE J0254+0223 and WISE J1741+2553 — are at estimated distances of 15 and 18 light years respectively. Their strong infrared signature and their extremely faint appearance at visible wavelengths attracted the team’s attention, and both show the high proper motion across the sky that flags nearby stellar objects. The team was able to use the Large Binocular Telescope (LBT) in Arizona to determine spectral type and distance more accurately. Interestingly, both objects fit into the category of T-type brown dwarfs, at the boundary of the still not well defined class of Y-type brown dwarfs.

Image: The (un)known Solar neighbors. The stars are shown with symbols of different sizes and colours, roughly corresponding to their real sizes and spectral types. Most stars in the Solar neighborhood are red dwarf stars of spectral type M (in the middle of the figure) with surface temperatures of slightly more than 2000 Kelvin. Proxima, our nearest known neighbor, also belongs to this class. The number of brown dwarf discoveries (almost all with spectral types L and T, and surface temperatures below 2000 K) is already higher than the number of white dwarfs (shown as small white dots at the top). The two nearest brown dwarfs, epsilon Indi Ba and Bb, the discovery of which was reported by the AIP in 2003 and 2004, and the newly found objects are marked. (Credit: AIP).

Do brown dwarfs, hitherto undetected, surround us in large numbers? We certainly can’t rule out the possibility, and we can expect much more data mining from the riches WISE has accumulated. And yes, the case for a brown dwarf closer than the Alpha Centauri stars is still open, making the brown dwarf hunt of unusual interest for identifying potential targets for future probes. But the two brown dwarfs in question could prove useful in many ways in their own right, as the paper on this work notes:

While WISE J0254+0223 and WISE J1741+2553 are likely similar to the few other T8-T10 brown dwarfs known, they are the first ultracool brown dwarfs detected in both 2MASS and SDSS. With their relatively bright magnitudes they are excellent targets for detailed spectroscopic investigations and for high resolution imaging in search of possible binarity. They may become important laboratory sources at the boundary between the T-type and the suggested Y-type (Kirkpatrick et al. 1999) classes of brown dwarfs.

Image: False-colour images of the two brown dwarf discoveries WISE J0254+0223 and WISE J1741+2553 (composite of three images taken by the Wide-field Infrared Survey Explorer (WISE) with different filters in the infrared). In the WISE colours, the extremely cool brown dwarfs appear as yellow-green objects. The positions of the objects as observed by a previous near-infrared sky survey about ten years before the WISE observations are also marked. Every image covers a sky field about 200 times smaller than the full moon. After 700 and 1200 years, respectively, the proper motions of the two objects lead to a shift in their position as large as the full moon diameter. (Credit: AIP, NASA/IPAC Infrared Science Archive).

The paper is Scholz et al., “Two very nearby (d ~ 5 pc) ultracool brown dwarfs detected by their large proper motions from WISE, 2MASS, and SDSS data” (preprint).

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A Binary System on the Edge of Merger

by Paul Gilster on July 14, 2011

A pair of white dwarf stars too close together to distinguish visually may help us in the hunt for gravitational waves, while potentially explaining a whole class of rare, relatively faint supernovae. The system in question — called SDSS J065133.33+284423.3, or J0651 for short — was found during a spectroscopic survey looking for extremely low mass white dwarfs. J0651 includes one white dwarf with about a quarter of the Sun’s mass compacted down to Neptune-size, along with a companion white dwarf that is half the Sun’s mass and about the size of the Earth.

Usefully, this is a system oriented so that we can observe eclipses of each star by the other, which is how we can measure orbital parameters, masses and white dwarf radii. The General Theory of Relativity predicts that close pairs of stars produce gravitational waves that are ripples in the curvature of spacetime, and as the paper on the new work points out, the binary pulsar PSR B1913+16 has already given us indirect evidence for such waves through the gradual decay of the orbit as predicted by Einstein’s theory. J0651 now emerges as an opportunity to study gravitational waves again by measuring small changes in the stars’ orbital periods.

Image: Two white dwarfs have been discovered on the brink of a merger. In just 900,000 years, material will start to stream from one star to the other (as shown in this artist’s conception), beginning the process that may end with a spectacular supernova explosion. Watching these stars fall in will allow astronomers to test Einstein’s general theory of relativity as well as the origin of a special class of supernovae. Credit: David A. Aguilar (CfA)

Thus we have an unusually useful celestial laboratory. Because there seems to be no exchange of mass, the change in separation over time should be easy to measure. From the paper:

We…predict that J0651’s orbital period is shrinking by 2.7 × 10-4 sec per year due to gravitational wave radiation. The expected change in period adds up to a 5.5 sec change in time-of-eclipse in one year. When we measure this change we expect to provide yet another fundamental test of general relativity and the existence of gravitational waves.

It’s a test that could potentially be confirmed by the proposed ESA/NASA Laser Interferometer Space Antenna (LISA) mission, which the authors predict could detect this gravitational wave source within its first week of operation considering its peak sensitivity at frequencies corresponding to orbital periods like those found here. The white dwarfs complete an orbit in just 13 minutes and will merge quickly in astronomical time. On that issue the paper comments:

The absence of mass transfer in J0651 is perhaps surprising given how quickly it will merge. In all known binaries with periods comparable to J0651… one star fills its Roche lobe and transfers mass to its companion. Our data show that the J0651 primary has a Roche lobe radius 1.5 times its current radius. Under the assumption of energy and angular momentum loss due to gravitational wave radiation, the primary WD will reach its Roche lobe radius at an orbital period of 6.5 minutes in 0.9 Myr.

What happens when the stars merge 900,000 years from now is another issue. In some models, merging white dwarf pairs are the source of faint stellar explosions called underluminous supernovae. Such objects are 10 to 100 times less luminous than normal Type Ia supernovae. The supernova SN 2005E, for example, can be explained using parameters similar to the J0651 system, but mass transfer between the two stars could lead to a variety of different outcomes. Thus the need for the ongoing survey of low mass white dwarf systems using the MMT telescope at the Whipple Observatory on Mt. Hopkins, Arizona, from which the current paper draws its data.

The two white dwarfs are circling at a speed of some 600 kilometers per second. “If there were aliens living on a planet around this star system, they would see one of their two suns disappear every 6 minutes – a fantastic light show.” said Smithsonian astronomer and co-author Mukremin Kilic. So strong is the mutual gravitational pull of the white dwarfs here that the lower-mass star is deformed by three percent and, as this Harvard-Smithsonian Center for Astrophysics news release notes, a similar bulge on our own planet would result in tides 190 kilometers high.

The paper is Brown et al., “A 12 minute Orbital Period Detached White Dwarf Eclipsing Binary,” accepted by Astrophysical Journal Letters and available as a preprint.

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A Neptunian Year Considered

by Paul Gilster on July 13, 2011

When the German astronomer Johann Gottfried Galle discovered Neptune on September 23, 1846, he found a world so distant from the Sun that its orbit takes 165 years to complete. With Neptune reaching its first complete revolution since discovery, an event that occurred yesterday, we can enjoy some celebratory Hubble imagery of the planet. I especially like the shot below, which not only shows atmospheric features but also has been tweaked to reveal some of Neptune’s moons. The planet has about thirty moons, most of them too faint to appear in these images.

Image: This illustration was composed from numerous separate Hubble Wide Field Camera 3 images. A color image composed of exposures made through three color filters shows the disk of Neptune, revealing clouds in its atmosphere. Forty-eight individual images from a single filter were brightened to reveal the very faint moons and composited with the color image. The white dots are Neptune’s inner moons moving along their orbits during Hubble’s observations. The solid green lines trace the full orbit of each moon. The spacing of the moon images follows the timing of each Hubble exposure. Triton, in the lower left corner, is the brightest of the moons seen in these images, farthest from the planet, and moves in a counter-clockwise sense in this view. Next closest to Neptune is Proteus, followed by Larissa, Galatea and Despina, all of which move clockwise in this view, opposite to Triton’s (retrograde) motion. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

The four images below were taken with Hubble’s Wide Field Camera 3 in late June, spaced at four hour intervals to offer a full view of the planet’s 16-hour rotation. You can make out high-altitude clouds of methane ice crystals in the northern and southern hemispheres. And just as we’ve recently looked at seasonal changes on Saturn, the Hubble imagery reveals similar changes on Neptune, with cloud activity shifting to the northern hemisphere. The southern hemisphere is now in early summer, while the northern hemisphere has entered winter. Neptune has an axial tilt of 29 degrees, creating seasons that last for some forty years each.

Image: In the Hubble images, absorption of red light by methane in Neptune’s atmosphere gives the planet its distinctive aqua color. The clouds are tinted pink because they are reflecting near-infrared light. A faint, dark band near the bottom of the southern hemisphere is probably caused by a decrease in the hazes in the atmosphere that scatter blue light. The band was imaged by NASA’s Voyager 2 spacecraft in 1989, and may be tied to circumpolar circulation created by high-velocity winds in that region. The temperature difference between Neptune’s strong internal heat source and its frigid cloud tops, about minus 260 degrees Fahrenheit, might trigger instabilities in the atmosphere that drive large-scale weather changes. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

The story of Neptune’s discovery is a fascinating topic in itself. Galileo actually recorded Neptune in his notebooks but didn’t follow up the observation. British astronomer William Herschel would later note that the orbit of Uranus did not behave as expected according to Newton’s laws, leading to speculations (like those of French astronomer Alexis Bouvard in 1821) that another planet was tugging at Uranus. Both Urbain Le Verrier and John Couch Adams predicted the location of the putative planet in the 1840s, but it was Le Verrier who described his prediction to Galle at the Berlin Observatory. After that, it was a matter of two nights of observation before Galle was able to identify the planet. Although the Royal Society would award Le Verrier the Copley Medal for his work, supporters of Adams defended his right to be considered a co-discoverer. Recent work has cast doubt on the idea.

Neptune makes numerous appearances in science fiction, such as Samuel Delany’s Triton (1976) and Jeffrey Carver’s Neptune Crossing (1994), in both of which much of the action takes place on Neptune’s largest moon. But earlier appearances are interesting, including Olaf Stapledon’s Last and First Men (1930), in which the planet serves as humanity’s final home. H.G. Wells likewise wrote about Neptune in ‘The Star’ (1897), a short story in which the planet is destroyed by a collision with what appears to be a rogue wandering planet from the interstellar deep. The event puts a brilliant new star in Earth’s sky, one that inexorably approaches our planet. Interestingly, the massive new object now gets a gravitational assist from Jupiter, as foreseen by a canny mathematician who forecasts the end of the human race:

The new planet and Neptune, locked in a fiery embrace, were whirling headlong, ever faster and faster towards the sun. Already every second this blazing mass flew a hundred miles, and every second its terrific velocity increased. As it flew now, indeed, it must pass a hundred million of miles wide of the earth and scarcely affect it. But near its destined path, as yet only slightly perturbed, spun the mighty planet Jupiter and his moons sweeping splendid round the sun. Every moment now the attraction between the fiery star and the greatest of the planets grew stronger. And the result of that attraction? Inevitably Jupiter would be deflected from its orbit into an elliptical path, and the burning star, swung by his attraction wide of its sunward rush, would “describe a curved path” and perhaps collide with, and certainly pass very close to, our earth. “Earthquakes, volcanic outbreaks, cyclones, sea waves, floods, and a steady rise in temperature to I know not what limit”–so prophesied the master mathematician.

‘The Star’ is still a good read (Wells’ Martians even make an appearance). You can read it online here, an enjoyable way to celebrate Neptune’s first full year since discovery.

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Supernovae: Factories of Cosmic Dust

by Paul Gilster on July 12, 2011

The supernova called SN 1987A is a prime object for scrutiny because it gives us the chance to see the various phases of stellar death over time. And as you might guess from the fact that it was visible to the naked eye when first detected back in 1987, it’s located relatively nearby, in the Large Magellanic Cloud. Working in the far-infrared, the European Space Agency’s Herschel space observatory has made new discoveries about SN 1987A while studying this small galaxy’s cold dust emissions.

The surprise result: SN 1987A is shrouded with enormous amounts of dust, 10,000 times more than previous estimates. The dust was at a temperature of roughly minus 256 to minus 249 degrees Celsius, making it a bit colder than Pluto (minus 240 degrees Celsius). These are the first far-infrared observations of this object, showing that the dust is emitting more than 200 times the energy of the Sun. Moreover, there is enough dust here to account for 200,000 planets the size of the Earth. Thus we learn that supernova explosions can be true dust factories.

Looking at SN 1987A with different instrumentation has proven valuable. The image below contrasts what Herschel can see versus the view from the Hubble Space Telescope. Here we’re contrasting Hubble with Herschel’s ability to see much longer wavelengths, and gaining a broad, composite picture of supernova dust formation.

Image: This layout compares two pictures of supernova remnant SN 1987A — the left image was taken by the Herschel Space Observatory, and the right is an enlarged view of the circled region at left, taken with NASA’s Hubble Space Telescope. The tiny pink ring in the Hubble image shows where a shock wave from the blast is hitting the surrounding material expelled from the star before the explosion. The cause for the outer, faint rings is unknown. When Herschel observed SN 1987A, it saw something different. Herschel sees infrared and submillimeter light, much longer in wavelength than the visible light Hubble detects. For this reason, its picture of the supernova is not as sharp, appearing only as a fuzzy dot inside the circle. But that dot represents an important discovery of vast reservoirs of cold dust around SN 1987A. Herschel can see very cold material — the colder something is, the longer the wavelengths of light it emits. Credit: ESA/NASA-JPL/UCL/STScI.

We need to learn as much as we can about cosmic dust because the heavy atoms — carbon, silicon, oxygen, iron — that it contains were not produced in the Big Bang but later. These elements are major constituents of the rocky planets and key players in life itself. And while old red giant stars in today’s universe are thought to be major dust producers as their gases flow outward from the star, they would not have been present for this purpose in the very early universe. But dust condensing from the gaseous debris of a supernova would have become available early on, accounting for the dust seen in young galaxies observed at huge distances from Earth.

“The Earth on which we stand is made almost entirely of material created inside a star,” explained the principal investigator of the survey project, Margaret Meixner of the Space Telescope Science Institute, Baltimore, Md. “Now we have a direct measurement of how supernovae enrich space with the elements that condense into the dust that is needed for stars, planets and life.”

We also see the value of probing the universe with different wavelengths, such as Herschel’s far-infrared. While we’ve had previous studies on supernovae and their ability to produce dust (NASA’s Spitzer Space Telescope, working with shorter infrared wavelengths than Herschel, found 10,000 Earth masses of fresh dust around the supernova remnant called Cassiopea A), this detection of a much larger reservoir of dust around SN 1987A confirms and extends our knowledge. The closest supernova witnessed in almost 400 years has proven a useful object indeed.

The paper is Matsuura et al., “Herschel detects a massive dust reservoir in supernova 1987A,” published in Science Express on 7 July 2011 (abstract). More in this JPL news release.

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Report from the UK Space Conference

by Paul Gilster on July 11, 2011

By Rob Swinney

Rob Swinney is a freelance writer, a member of the British Interplanetary Society and an active participant in the Tau Zero Foundation/BIS study group Project Icarus, a team of volunteers working on a practical design for an interstellar probe. Rob completed his Bachelors degree in Astronomy and Astrophysics at the University of Newcastle Upon Tyne and his Masters in Radio Astronomy at the University of Manchester (Jodrell Bank). Later he graduated from Cranfield University (then the Cranfield Institute of Technology) with a Masters degree in Avionics and Flight Control Systems. After a rewarding career in the Royal Air Force as an Aerosystems Engineer (Avionics) Officer he completed his Commision in 2006 having attained the rank of Squadron Leader. He is a Chartered Engineer registered with the UK’s Engineering Council and a Member of the Institution of Engineering and Technology. Rob recently attended the UK Space Conference on July 4 and 5th and here offers us a personal view of the proceedings. Space agencies worldwide are challenged by budget cuts and the need to develop a new vision as we enter the age of commercial space. Our recent discussions here highlighted the problems of the US space program in particular. How do things look in the UK and the European Space Agency?

The UK Space Agency emerged from the forerunner British National Space Centre. This week the agency hosted the UK’s Space Conference 2011 at Warwick University, England, where economic issues came to the fore. The agency has an apparently vastly increased budget of several hundred millions of pounds although this was created by merging funds from other areas and the figure is still well below the amounts spent by the other major European economies.

The conference, whose theme was ‘The New Space Economy,’ brought together members of the space community from industry, government and academia and painted a positive picture of the space sector in the UK, which is estimated to be worth £7.5 billion per year (over $10 billion), a figure the new agency hopes to help grow to over £40 billion in the next 20 years. There was definitely a ground swell of positive opinion about the skills in the UK to build small satellites and other specific areas of the sector that can offer business opportunities.

Interestingly, David Willetts, a Member of Parliament and the UK Minister of State for Universities and Science, suggested the health of the UK space sector was in such a good state because there hadn’t been a government agency involved in the past and this had been to its advantage. It is perhaps unclear how ringing an endorsement this is of the move to governmental executive agency status. But Willetts did announce a number of policies to try and improve the environment for doing ‘space’ business in the UK, one of which was to lower the mandatory third party insurance limit from £100m to £60m (for launch and orbital operations).

Even if the agency just focuses on lowering costs and red tape there is little chance of the UK market not growing to £40 billion in the timeframe allowed given the rate of growth for the last 10 years – even through the recession we are now experiencing. Perhaps more challenging is the aim to grow the market share of worldwide space products and services from 6 to 10%.

What the Agency actually does with its £230 million budget is then open to debate. The good news for the European Space Agency (ESA) is that it looks like more of that money will end up being pushed through to ESA. The bad news is that it is really not a lot of money anyway and only a fraction of the totals of other European countries such as France and Germany. Even so, the importance of the UK involvement with ESA was apparent from the first session, ‘Space Policy,’ which included the ESA Director General Jean-Jacques Dordain, who helped set the scene. Dordain stated that although the conference had started on America’s Independence Day, “Together we are better.” Independent agencies cooperating skillfully can achieve much.

Various tracks were offered in the parallel sessions and on the first day I attended the ‘Science and Exploration’ session followed the next day by ‘Student presentations’ and then ‘Access to Space.’ There was an interesting mix. Much in evidence was the prototype British eccentric, perhaps a throw-back from an earlier age of brilliant endeavour but also a marker for the new generation of young enthusiasts fronted by UKSEDS, the UK chapter of the Students for the Exploration and Development of Space. Also in evidence were the hard headed business people who play so significant a role in the success and focus of the space business in the UK.

The second day opened with a panel session on ‘Innovation – Science, Business and Technology’ and included UK industry ‘giant’ Sir Martin Sweeting OBE, the executive chairman of Surrey Satellite Technology Ltd., along with innovator Alan Bond, Managing Director of Reaction Engines Ltd. and a key player in the original Project Daedalus starship design.

Bond discussed the challenges facing an innovator, especially when working with game-changing technology. This is clearly not a UK-specific issue, but he did lament the lack of support from government, industry and the banks, while noting the many skills and commitments innovators had to excel at in addition to their expertise in their field (e.g. becoming brilliant at presenting and communicating the idea, attending conferences at their own expense, working with economists and creating business plans, negotiating patent law as well as being a technical expert).

Bond said that innovators were usually young and naïve and would find that they had to live with less and less of the financial rewards of their innovation. I’m not sure if he was thinking of himself and the Reaction Engines Skylon spaceplane and its SABRE engine but he did mention that the technology first appeared some 40 years ago and that it has been fully 29 years since the start of the development. Perhaps the most valuable lesson he gave was perseverance!

Image: Skylon is the design for an unmanned, reusable spaceplane intended to provide low-cost access to space. The SABRE engines that would drive it offer both air-breathing and conventional rocket capabilities, the intent being to reach orbit in a single stage. Skylon is currently in its proof-of-concept phase. Is this the low-cost way to LEO we once imagined the Space Shuttle would be? Credit: Reaction Engines Ltd.

It is perhaps unclear how the UK Space Agency might have changed this process as its focus is on partnering with others and possibly some small independent projects.

It doesn’t look like there are any immediate plans to support blue sky thinking as far out as interstellar flight. Project Icarus may have to continue on its voluntary way. Indeed I heard interstellar distances mentioned only once and then only as a way of illustrating relative distances — e.g. if you imagine the Earth about the size of a large grapefruit, then the distance from Earth to our Moon is about 4m (a scale of 1,000,000:1), making the distance to the nearest stars the distance of the actual Moon, some 250,000 miles away. An interstellar conference this was not, but full marks to the organisers for putting together a successful look at current policy.

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Saturn: A Turbulent Early Spring

by Paul Gilster on July 7, 2011

I had been intending to cover recent news about Saturn in an upcoming post anyway, but the images below sealed the deal. They’re further wonders from Cassini, pictures of a massive storm in Saturn’s northern hemisphere that encircles the planet. First detected on December 5, 2010, the storm has been on the rampage ever since at about 35 degrees north latitude. It covers approximately 4 billion square kilometers. Cassini’s radio and plasma wave science instrument has been showing a lightning flash rate 10 times that of any other storms the spacecraft has monitored since its arrival in Saturn orbit back in 2004. The flashes were so frequent at one point that Cassini could no longer resolve individual strokes, although the intensity has now eased.

Image: The huge storm churning through the atmosphere in Saturn’s northern hemisphere, seen here in a true-color view from NASA’s Cassini spacecraft. This view looks toward the sunlit side of the rings from just above the ring plane. The image, captured on Feb. 25, 2011, was taken about 12 weeks after the storm began, and the clouds by this time had formed a tail that wrapped around the planet. Some of the clouds moved south and got caught up in a current that flows to the east (to the right) relative to the storm head. This tail, which appears as slightly blue clouds south and west (left) of the storm head, can be seen encountering the storm head in this view. Credit: NASA/JPL-Caltech/SSI.

It’s interesting to realize that the shadow cast by Saturn’s rings has strong effects on the planet’s weather. This storm is 500 times the area of the largest southern hemisphere storms Cassini has seen on its mission, and scientists are suggesting that we are now seeing such powerful storms in the northern hemisphere because of the change of seasons after the planet’s 2009 equinox. At present, Saturn is entering early northern spring, making this a relatively early storm. In previous years, Earth-based astronomers as well as Hubble have observed huge storms called ‘Great White Spots’ in late northern summer, some of which were as large as this one. Unfortunately, we didn’t have Cassini or Voyager on the scene for previous storms of this magnitude.

“This storm is thrilling because it shows how shifting seasons and solar illumination can dramatically stir up the weather on Saturn,” said Georg Fischer, a radio and plasma wave science team member at the Austrian Academy of Sciences in Graz. “We have been observing storms on Saturn for almost seven years, so tracking a storm so different from the others has put us at the edge of our seats.”

We’re looking at a storm that covers an area eight times the surface area of Earth. Since its arrival, Cassini has detected 10 lightning storms on Saturn, found in an area of the southern hemisphere now known as ‘Storm Alley.’ We’re now getting a glimpse of just how lively a Saturnian spring can be as the Sun’s illumination of the hemispheres changes. The storm is generating huge amounts of radio noise from lightning. At issue is the sudden release of such energies, unlike what we see on Jupiter or, for that matter, the Earth, where numerous storms are active at any given moment. In sharp contrast, Saturn seems quiet for years and then erupts into frenzied activity.

Image: False-color images from Cassini showing clouds at different altitudes. Clouds that appear blue here are the highest and are semitransparent, or optically thin. Those that are yellow and white are optically thick clouds at high altitudes. Those shown green are intermediate clouds. Red and brown colors are clouds at low altitude unobscured by high clouds, and the deep blue color is a thin haze with no clouds below. The base of the clouds, where lightning is generated, is probably in the water cloud layer of Saturn’s atmosphere. The storm clouds are likely made out of water ice covered by crystallized ammonia. Taken about 11 hours — or one Saturn day — apart, the two mosaics in the lower half of this image product consist of 84 images each. The mosaic in the middle was taken earlier than the mosaic at the bottom. Both mosaics were captured on Feb. 26, 2011, and each of the two batches of images was taken over about 4.5 hours. Credit: NASA/JPL-Caltech/Space Science Institute.

The storm on Saturn made the cover of Nature this week. The papers involved are Sánchez-Lavega et al., “Deep winds beneath Saturn’s upper clouds from a seasonal long-lived planetary-scale storm,” Nature 475 (7 July 2011), 71-74 (abstract) and Fischer et al., “A giant thunderstorm on Saturn,” Nature 475 (7 July 2011), 75-77 (abstract).

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