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This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.
When I was young, the only planets we knew about were the ones in our own solar system.
Astronomers presumed that many of the other stars in the night sky had planets too, but this was sheer speculation. We could never know for sure, the thinking went, because such planets were ridiculously small and faint. To ever see or study them seemed a complete impossibility. "Extrasolar planets," or "exoplanets," were a staple of science fiction, but not of professional astrophysics.
It's hard to believe that there was once such a simple time. The first definitive detection of an exoplanet was in 1991, identified by the tiny wobbles experienced by the parent star as its exoplanet swung around it. Since then, the field has exploded. There are now around 1,600 confirmed exoplanets, with almost 4,000 other known candidates. There are exoplanets smaller than Mercury, and others many times bigger than Jupiter. Their orbits around their parent stars range from a few hours to hundreds of years. And the ones we know about are just a tiny fraction of the approximately 100 billion exoplanets we now believe are spread throughout our Milky Way galaxy.
But while the golden age of exoplanets has barely begun, an exciting additional chapter is also taking shape: the hunt for exomoons.
An exomoon is a moon orbiting a planet, which in turn is orbiting another star. You may not have ever heard of exomoons before now. But if you're a fan of films such as "Avatar," "Return of the Jedi" or "Prometheus," this should be familiar territory: in all three cases, most of the action takes place on an exomoon.
But what about real life? How many exomoons do we know of? At the moment, zero.
Endor: not all exomoons come with ewoks.
Credit: Star Wars: Episode VI Return of the Jedi
But the race is on to find the real-life analogs of Endor and Pandora.
You might think searching for tiny rocks orbiting distant planets around faint stars hundreds or thousands of light years away is the ultimate example of an obscure academic pursuit. But exomoons are poised to become a big deal.
The whole reason exoplanets are exciting is that they're a path to answering one of the grandest questions of all: "Are we alone?" As we find more and more exoplanets, we eagerly ask whether life could exist there, and whether this planet is anything like Earth. However, so far we've yet to find an exact match to Earth, nor can we yet really know for sure whether any exoplanet, Earth-like or otherwise, hosts life.
There are several reasons why exomoons, these little distant worlds, may be the key to finding life elsewhere in the universe.
First, there's the stark reality that life on Earth may not have happened at all without the starring role played by our own moon.
The Earth's axis is tilted by 23.5 degrees relative to its motion around the sun. This tilt gives us seasons, and because this tilt is relatively small, seasons on Earth are mild: most places never get impossibly hot or unbearably cold. One thing that has been crucial for life is that this tilt has stayed the same for very long periods: for millions of years, the angle of tilt has varied by only a couple of degrees.
What has kept the Earth so steady? The gravity of our moon.
In contrast, Mars only has two tiny moons, which have negligible gravity. Without a stabilizing influence, Mars has gradually tumbled back and forth, its tilt ranging between 0 and 60 degrees over millions of years. Extreme changes in climate have resulted. Any Martian life that ever existed would have found the need to continually adapt very challenging.
Without our moon, the Earth, too, would likely have been subject to chaotic climate conditions, rather than the relative certainty of the seasons that stretches back deep into the fossil record.
The gravity of the moon also produces the Earth's tides. Billions of years ago, the ebb and flow of the oceans produced an alternating cycle of high and low salt content on ancient rocky shores. This recurring cycle could have enabled the unique chemical processes needed to generate the first DNA-like molecules.
Moons might contribute to a planet's habitability.
Credit: NASA/JPL-Caltech/Space Science Institute, CC BY-ND
Overall, as we continue to hunt for another Earth somewhere out there, it seems likely that a twin of Earth, but without a moon accompanying it, would not look familiar. Finding exomoons is a key part of finding somewhere like here.
Meanwhile, we shouldn't be discouraged by the fact that most exoplanets found so far are bloated gaseous beasts, with hostile environments unlikely to support life as we know it. What we don't know yet, crucially, is whether these exoplanets have moons. This prospect is exciting, because exomoons are expected to be smaller rocky or icy bodies, possibly hosting oceans and atmospheres.
This is hardly speculation: Titan (a moon of Saturn) has a thick atmosphere even denser than Earth's, while underground oceans are thought to exist on Enceladus (another moon of Saturn) and on Europa and Ganymede (both moons of Jupiter). Thus, if there is any other life out there somewhere, it may well not be found on a distant planet, but on a distant moon.
The hunt is on. While exomoons are too faint to see directly, astronomers are deploying ingenious indirect techniques in their searches. Those moons are assuredly out there by the billions – and soon we will find them. It won't be too much longer before these tiny worlds help us answer huge questions.
Bryan Gaensler, Director, Dunlap Institute for Astronomy and Astrophysics, University of Toronto
- See more at: http://www.space.com/31982-eying-exomoons-in-the-search-for-e-t.html#sthash.hFj8h6i3.dpuf
A tsunami (plural: tsunamis or tsunami; from Japanese: 津波, lit. "harbor wave"; English pronunciation:/tsuːˈnɑːmi/) , also known as a seismic sea wave, is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami. Unlike normal ocean waves which are generated by wind or tides which are generated by the gravitational pull of the Moon and Sun, a tsunami is generated by the displacement of water.
Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves, although this usage is not favored by the scientific community because tsunamis are not tidal in nature. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called "wave train". Wave heights of tens of meters can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous and they can affect entire ocean basins; the 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean.
The Greek historian Thucydides suggested in his late-5th century BC History of the Peloponnesian War, that tsunamis were related to submarine earthquakes, but the understanding of a tsunami's nature remained slim until the 20th century and much remains unknown. Major areas of current research include trying to determine why some large earthquakes do not generate tsunamis while other smaller ones do; trying to accurately forecast the passage of tsunamis across the oceans; and also to forecast how tsunami waves interact with specific shorelines.
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Three potentially habitable Earth-size planets have been discovered orbiting a dim, cold nearby star that is barely larger than Jupiter, researchers say.
"These kinds of tiny, cold stars may be the places we should first look for life elsewhere in the universe, because they may be the only places where we can detect life on distant Earth-sized planets with our current technology," study lead author Michaël Gillon, an astronomer at the University of Liège in Belgium, told Space.com.
Astronomers focused on a star originally named 2MASS J23062928-0502285 that was discovered using TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope), a telescope in Chile. This dim cold red star, now known as TRAPPIST-1, is located in the constellation of Aquarius about 39 light-years from Earth. In comparison, Alpha Centauri, the nearest star system, is about 4.3 light-years from Earth.
In 1990, Voyager 1 captured the most distant portrait of our planet ever taken, revealing that from beyond Pluto's orbit, Earth appears as nothing more than a "pale blue dot." In a new study, researchers have tested whether Earth's color is a unique feature of life-friendly planets. If so, searching for exoplanets displaying this hue could help in singling out worlds potentially brimming with alien life.
As it turns out, Earth's delicate color can be closely mimicked by hypothetical exoplanet types that are completely uninhabitable. A broader portion of Earth's overall spectrum, however, does display a subtle signature only attributable, insofar as we know, to life. Seeking this signature from pale blue worlds in stars' habitable zones with future telescopes could be a powerful tool for identifying worlds deserving of intense further scrutiny.
"One important takeaway is that color should be used with caution because we found it's relatively easy to make lifeless planets that are pale blue in color," said lead author Joshua Krissansen-Totton, a doctoral student at the University of Washington. "With that said, I was very excited to find that Earth's spectrum has an intriguing signature that is biogenic, unique and potentially quite useful." [10 Exoplanets That Could Host Alien Life]
When viewed from deep space, like with and reduced to a single pixel or less, Earth appears its distinctive shade for several key reasons, the study explained.
Nitrogen, the overwhelming component of Earth's atmosphere, is transparent. An atmosphere that is clear to visible light preferentially scatters short wavelength, bluer light, as opposed to longer wavelength, redder light. As a result of this so-called Rayleigh scattering, blue light appears to come from all directions, and presto: the sky looks blue, as do the oceans. The blue light as well, and thus to external observers.
Earth's white clouds boost reflectivity at all wavelengths, diluting the intensity of the Rayleigh scattering. Some red light also mixes into Earth's color palette as it's reflected by the continental land masses. That redness bends Earth's overall color viewed from afar more toward the light blue than, say, the rich azure of Neptune, whose atmosphere's high methane levels absorb red and reflect blue.
Meanwhile, the oxygen in our air chemically reacts with many types of molecules that would otherwise form an opaque haze. Such atmospheric haze is evident in the visages of Venus, Jupiter, Saturn, and
Earth's free oxygen would not exist were it not for our planet's teeming plant and microbial life, which constantly replenish it through the process of photosynthesis.
This information in hand, the University of Washington researchers then compiled the spectra of various real and theoretical exoplanets.
"We set about trying to quantify Earth's color and compared it to that of other planets that were not habitable," said Krissansen-Totton.-
Will humanity find intelligent alien life anytime soon? Probably not, according to theoretical physicist Stephen Hawking.
Hawking made the prediction yesterday (April 12) during the announcement in New York City. At the news conference, Hawking, along with Russian billionaire investor Yuri Milner and a group of scientists, detailed a new project that aims to send a multitude of tiny, wafer-size spaceships into space to the neighboring star system Alpha Centauri.