Category: Astronomy

Extinctions and Space

There’s one sure way to spice up science headlines: add dinosaurs—and when you combine dinosaurs with space and exotic cosmology, you can’t go wrong.

Thirty years ago, a scientific hypothesis brought space and extinction together. Scientists noticed what appeared to be a regular repeating pattern of massive extinction events in Earth’s history, falling roughly every 26 million years. What could explain such a pattern? One possibility is that the cause lies in the ecosystems themselves: something about biological communities causes them to fail when they reach certain milestones. Another possibility is that the cause is external, resulting either from the geological processes of the Earth, or perhaps from something extraterrestrial.

Perhaps the most famous (though not the most severe) extinction event in history is the one that occurred at the end of the Cretaceous period and brought about the end of the dinosaurs; the evidence is now conclusive that a major meteor, asteroid, or comet impact near the present Yucatan played a decisive role in this extinction event. But if an impact event caused at least one major extinction event, could impacts be a more general cause of extinctions? Other evidence seemed to show, in addition to periodicity in extinctions, a similar periodicity of around 30 million years or so in the rate of impacts on the Earth’s surface. We thus have two pieces of evidence that fit together: extraterrestrial impacts and extinctions both occurring at similar intervals, the former being an obvious potential cause of the latter.

But what could cause impacts from space to occur in a regular pattern?

Periodicity is not uncommon in astronomy, and there’s an obvious source: orbits. Objects that travel in orbits around other objects naturally tend to display regular, periodic behavior. This line of thinking led to the proposal that it was in fact orbital motion that led to the regular peppering of Earth with extraterrestrial objects.

Far out beyond the orbit of the most distant planets lies the Oort cloud, a vast spherical region surrounding our Sun that is populated by icy bodies that, when they fall near the Sun, form comets. When the early solar system formed, the massive planets carved out a relatively clear bubble inside of which the Earth and the familiar planets orbit. The remaining debris ended up in one of three places: either sucked into the Sun or the forming planets, shepherded into the asteroid or Kuiper belts, or flung into the deep space of the Oort cloud. Every now and again, one of these Oort cloud objects comes falling into the inner solar system, appearing in our skies as a comet, but generally these bodies orbit slowly in the distant reaches, uninclined to make their way inwards.

Unless, that is, a gravitational tug upsets them, casting them in and out in showers of cosmic debris. This sort of gravitational tug can be given, for example, by a passing star—and it was just this realization that led, in 1984, to the suggestion that our Sun was not alone.

Instead, it was proposed that the Sun (like most stars in the galaxy) had a companion, a dim and distant dwarf (dubbed “Nemesis”) that followed in a wide orbit. Every thirty million years or so, Nemesis swung close enough in to the Oort cloud to scatter comets about, sending some of them inward on paths that would inevitably lead at least a few to impact the Earth. Thus, we find a pattern to impacts and, subsequently, extinctions on Earth.

In the years that followed, however, the Nemesis hypothesis foundered on the fact that no trace of the hypothetical star was found by any observations. The latest evidence supports the non-existence of Nemesis. A thorough examination of data from the WISE (Wide-field Infrared Survey Explorer) spacecraft, published just recently, found no bodies of significance out to 10,000 AU, and no signs of larger bodies at farther distances have been forthcoming. Nemesis was proposed as speculation, and a quarter century of observation has led to no observational support. The Sun, as far as we can tell, is alone, and no large planets or dwarf stars lurk beyond Neptune that could explain disturbances of the outer solar system that could lead to periodic comet showers.

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But that doesn’t leave us bereft of hypotheses. The newest idea to explain periodic comet showers has to do not with large bodies disturbing the Oort cloud with gravity, but rather with the motion of the entire solar system itself. What’s more, the newest iteration of this latest hypothesis invokes one of the hot topics of modern astrophysics, dark matter.

milky-way-galaxy_nature.jpg

Just as the planets of the solar system orbit the Sun, the Sun itself orbits the center of the Milky Way galaxy, making a giant circuit that takes hundreds of millions of years to complete. But unlike the fairly flat orbits of the planets, the Sun’s orbit is wavy, coasting up and down through the plane of the galaxy. The reason for these waves is that the galaxy’s disk contains a significant amount of mass: as the Sun drifts upwards, the galaxy’s mass pulls it back down, until it plunges through the disk and emerges on the other side, drifting away until gravity pulls it back, repeating the process over again.

As it turns out, the period of this motion above and below the galactic plane appears to be about seventy million years, meaning that the solar system passes through the galactic plane about every—you guessed it—thirty-five million years or so, notably close to the purported period of increased impacts and extinctions. That period alone is enough to be suspicious; it may very well be that the ordinary gravitational disturbance of passing through the plane alone is enough to upset the distant solar system. The newest examination of the theory, however, invokes the latest speculative physics. Dark matter is a proposed form of matter that makes up the bulk of the universe and that interacts with normal matter in ordinarily negligible ways; there is no known means of detecting dark matter directly, but it is invoked to explain a number of observations that cannot be explained by normal matter alone.

Suppose, then, a new paper asks, that not only does the galactic disk contain a high concentration of normal matter, but it might contain disks of dark matter as well, and as the solar system plunges through these disks on its rising and falling track around the galaxy, it is this dense dark matter that causes icy comets to be scattered and sent to collide with the Earth.

Perhaps. Or perhaps motion through the galaxy alone is enough, even without dark matter, to account for the solar system’s disturbance. Or, it could be that we’re chasing phantoms—the statistical detection of impact periodicity and extinction patterns is weak: maybe there really is no periodicity to be explained. As always in science, time will give us more to consider.

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Image: Nature/C. Carreau-ESA

Lunar Meteor Strike

Last September, a roughly meter-wide meteor struck the Moon, creating an explosive impact that would have been visible to the naked eye (although it’s unclear whether anyone actually saw it), and which was captured on video (above). A study of the impact has just been published in Monthly Notices of the Royal Astronomical Society. Astronomers calculate that the impact created a 50-m-wide crater, which may be imaged by lunar orbiters in the future. Read more about this story at Nature.

Asteroid Flyby Tonight

An 885-foot-diameter asteroid will fly by the Earth tonight (Monday, February 17th, 2014) at a distance of just over 2 million miles. At this distance it presents no threat to the Earth, but the Slooh online observatory will be hosting a webcast with telescopic views of the flyby along with commentary from astronomers.

Slooh’s online webcast will begin at 9 p.m. EST.

Time & Space

 

SN 2014J in colour (University College London)

Twelve million years ago, a star in the galaxy we call M82 exploded. Since M82 lies 12 million light years away, the light from that explosion just reached Earth last week, being first noticed on January 21st. You may be able to see this supernova for yourself. M82 sits high in the northern sky above the Big Dipper. As of yesterday, Sky & Telescope reports the supernova’s magnitude at 10.6, within the range of backyard telescopes. The explosion was spotted serendipitously on January 21st by a group of undergraduate students and their teacher during a brief workshop at University College London.

One of the aspects that I find most interesting about this process is the extreme juxtaposition of scales of time and space. As noted, the galaxy M82 sits 12 million light years away; therefore, the light from the supernova explosion has taken 12 million years to reach us. Yet compare these huge numbers with the supernova itself: the explosion itself lasted only a matter of seconds. A Type Ia supernova, like this one, occurs when a compact white dwarf star pulls matter (via gravity) off of a much larger companion star. Eventually, enough mass accumulates on the white dwarf so as to suddenly initiate fusion, explosively releasing tremendous amounts of energy. The explosion itself lasts for a minute or so, and the brightly glowing aftermath itself persists for weeks (which at least gives us plenty of time here to catch it). Yet this brief event sheds light and energy out into space that can overpower the luminosity of an entire galaxy and can be seen in skies of a planet—our planet—millions of light years distant and millions of years in the future.

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I have not yet read it, but David Bentley Hart’s new book The Experience of God sounds promising. William Carroll reviews it at Public Discourse, and Edward Feser reacts to Jerry Coyne’s comments on it here. Hart writes:

“Any argument for or against the reality of God not so understood—any debate over an intelligent designer, or a supreme being within time and space who merely supervises history and legislates morals, or a demiurge whose operations could possibly be rivals of the physical causes describable by scientific cosmology—may prove a diverting amble along certain byways of seventeenth-century deism or eighteenth-century “natural history,” but it most definitely has nothing to do with the God worshiped in the great theistic religions or described in their philosophical traditions, or reasoned toward by their deepest logical reflections upon the contingency of the world.”

And Carroll adds:

“Hart offers mostly dialectical arguments to show the incoherence of the positions he rejects. We recognize the radical contingency of the world we experience, a recognition that is not the result of a demonstrative argument but a kind of intellectual intuition based on the immediacy of our experience. This insight into the ‘absolute contingency’ of the world eludes those who embrace a materialistic metaphysics. It is also the basis for a reflection that leads to God as the absolutely necessary being.”

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In honor of St. Thomas Aquinas’ recent feast day, we have this—over at BioLogos, Fr. Austriaco argues that evolution is a fitting means of creation:

“I propose that it was fitting for God to have created via evolution rather than via special creation because in doing so, he was able to give his creation – the material universe and the individual creatures within it – a share in his causality to create. In this way, he more fully communicates his perfection to his creation, thus, more clearly manifesting his glory. As St. Thomas points out: ‘If God governed alone, things would be deprived of the perfection of causality. Wherefore all that is effected by many would not be accomplished by one.’ (Summa theologiae, I.103.6)”

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Stephen Hawking announces that he suspects that black holes aren’t quite what he thought they were. To wit: he thinks that the event horizon has been mischaracterized. Classically, the event horizon marks the point of no return: the line at which the black hole’s gravity becomes inescapable. Once it is crossed, there’s no way out again. Interestingly, though, in the classical view, an astronaut crossing the event horizon wouldn’t notice anything different at first. He’d just ride along across it along with everything else traveling with him. More recent quantum mechanics–based analyses, however, have suggested that the event horizon is marked by a “firewall” of astoundingly high energy created by quantum behavior at the black hole’s boundary. But Hawking now says that the whole idea of the horizon needs to be evaluated. Other physicists remain skeptical.

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And, finally, Pope Francis encourages Notre Dame to resist attempts to undermine the university’s commitment to Catholic moral practice.

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Image: University College London

Impressive Andromeda

moon_andromeda.jpg.CROP.original-original

Phil Plait (Bad Astronomy) shares this picture that has been making the rounds lately, ostensibly showing the Andromeda galaxy as it would appear in our sky if it were significantly brighter. The Moon serves to give a sense of scale, and given how big the Moon appears in our sky, seeing the Andromeda galaxy next to it is surprising. Analysing it with his usually debunking determination, Phil concludes that the picture is in fact just about right. Although the brightness is manipulated, the size of the Andromeda Galaxy is accurately presented.The Andromeda galaxy really is this big in our sky, it’s just that it’s too dim to see like this in all its glory.

The Andromeda galaxy (M31) lies about 2.5 million light years away in the direction of the constellation Andromeda. It is the nearest large spiral galaxy to our own – and is getting closer, with the Milky Way and Andromeda expected to collide is some four billion years.andromeda galaxy

I love pictures like these because the reveal just how grandiose the beauties of the night sky are, despite their seeming hiddenness. (For another example, see here.) For most people today, the night sky is obscured behind the glare of city lights, TV screens, and smartphones. But even for people more familiar with the sights of the night sky, it is easy to forget that these images are not obtained by hopping in the Enterprise and warping light years away. They are, for the most part, images taken by telescopes on the Earth, or at least in Earth orbit, and the objects they present are impressively present in the sky just outside our windows if we just know how to look at them in the right way.

Fortunately, although Andromeda is not as bright as this picture shows, it is this big, and it is relatively easy to find—and this time of year is prime Andromeda viewing time. In dark enough skies, you can see it with the naked eye, and all that is needed to bring it out more obviously viewing is a pair of binoculars or a small telescope. In January, Andromeda (the constellation) sits fairly high in the western sky in the evening. The Andromeda galaxy lies between the bottom of the sideways “W” created by the constellation Cassiopeia and the line formed by the three bright stars in Andromeda itself. For more about how to find it, see here.

Images: Unknown, via Bad Astronomy; Stellarium

Geminids Meteors Peak Tonight

From Sky & Telescope:

“It’s time again for the Geminids, one of the year’s best meteor showers. There’ll be interference from moonlight this year, but you’ll still probably see plenty of these “shooting stars.”

Although they can appear anywhere in the night sky, Geminid meteors appear to radiate from the constellation Gemini, which is well above the horizon by late evening.

In mid-December every year Earth passes through the Geminid meteoroid stream. The resulting meteor shower is unusual in several ways. It’s often the richest reliable shower of the year, and it seems to be strengthening over the decades. It becomes nicely active as early as mid-evening, so you don’t have to wait until after midnight (as is the case with many other showers). Its meteors are relatively slow, arriving at 36 km (22 miles) per second, hardly more than half the speed of the Perseids, Orionids, and Leonids. Also, these meteors often appear yellowish, and their deep plunges into the atmosphere betray them as dense bits of rock rather than fluffy dust clods like most cometary meteors.”

Read here.

The Earth and the Moon

A theory explaining the origin of the Moon needs to take into account three things: (1) the physical characteristics of the Earth–Moon system, i.e., why the Earth and Moon orbit the way they do; (2) the similarities in the Earth’s and the Moon’s compositions; and (3) the differences in composition. Each consideration alone is easy enough to account for, but combining all three can be challenging. If the Earth and the Moon were utterly different, it would be easy to suppose they formed separately and the Moon was captured by the Earth. Alternatively, if they were exactly similar, it would be easy to suppose they had somehow formed simultaneously from the same source material.

As it turns out, the Moon matches the composition of the Earth’s crust and mantle fairly well, while overall the Moon lacks the Earth’s iron content—and on Earth, the most iron-rich portion of the planet is its interior.

The most commonly accepted theory is that a hypothetical, approximately Mars-sized body called Thea struck the Earth obliquely early in the solar system’s formation, knocking off a significant portion of the mantle, while leaving the iron-rich core relatively intact. The resulting debris from the Earth’s mantle and the remnants of Thea formed the Moon and settled back on the Earth’s remaining surface, accounting for the similarity between the two.

Sounds good as far as it goes, but to stand up, the theory needs to account for the Earth’s rotation and the Moon’s orbit, as well as allow for sufficient mixing between Thea and the material blasted off the early Earth so as to eliminate any noticeable difference in composition.

This article from Nature details some of the latest considerations in evaluating this theory.

Meanwhile, the Juno spacecraft has returned a new video, shown above, of the Earth-Moon system, showing both objects in motion. Juno is heading for Jupiter, but used an Earth flyby on October 9th to gain speed on its way. Read more about the video here.

Video: NASA/JPL

CNA Interviews Vatican Astronomer Br. Consolmagno

Br. Guy Consolmagno (CNA)
Catholic News Agency has interviewed Brother Guy Consolmagno, S.J., who works at the Vatican Observatory, and is known for his science communcation work:

“The astonishing thing to me about astronomy is not only that the universe makes sense and I can come up with equations and explain it,” he continued, “but the way it makes sense is beautiful.”

“God chose to create a universe that was at the same time logical and beautiful, one that I can enjoy with my brain and enjoy with my heart,” he stressed, going on to say that this “tells me something about who God is and how He creates and how He’s expecting me to relate to Him.”

Addressing the fact that many are surprised at the existence of the Vatican Observatory, Br. Consolmagno stated that “that’s part of the reason we exist; to surprise people.”

“To make people realize that the church not only supports science, literally… but we support and embrace and promote the use of both our hearts and our brains to come to know how the universe works.”

Read here.

 

Image: Catholic News Agency

ISON Monday

ISON from SDO, in December(NASA)

Here are the latest ISON images from SOHO. The comet now definitely appears to have been disrupted by its pass near the Sun, leaving little more than a dust cloud behind. Updates are available from Sky & Telescope.

What Happened to ISON?

ISON Survives, from SOHO (NASA)

Comet ISON made its closest approach to the Sun yesterday, and it’s not quite clear yet in just what form the comet has emerged from its close encounter. Comets are composed of conglomerations of ice and rock, and exposure to the Sun’s intense heat and gravity during close passes can tear them apart. The comet’s nucleus orbits the Sun like any other solid solar system body, while the gas and dust of the coma and tail make up the dramatic, visible portion of the comet as they are blasted off the nucleus by solar heat and pressure. During live observations with NASA’s SDO satellite yesterday, observers did not see ISON come back into view as expected—in fact, it was surprisingly not seen by SDO at all. The suspicion began to grow that the comet hadn’t survived in any meaningful state. Later, however, SOHO images (above) revealed that something had survived, as an obvious cloud emerged from near the Sun, following ISON’s orbital path. But there is still not enough evidence to make any confident judgments about what this post-encounter ISON is. Clearly, ISON in some form is now headed away from the Sun, but whether it is ISON’s nucleus, substantially intact, or scattered fragments, like the famous Shoemaker-Levy 9, remains to be seen.

Updates are available from NASA and from the Bad Astronomer Phil Plait.

Image: NASA