The First Aliens We Discover May Be Purple

In our quest to discover strange new life on strange new worlds, a group of astronomers has modeled potential alien worlds using Earth’s biological history as a framework. From this they have determined that if we are to detect extraterrestrial biology, we should fine-tune our search to the color purple.

Top Exoplanets for Alien Life

As we discover more and more worlds orbiting other stars in ever more biologically-pleasing orbits, the question “are we alone?” becomes increasingly acute. It’s inevitable that we will soon discover an alien world with Earth-like dimensions, orbiting a sun-like star within its habitable zone. But until we develop the means to remotely probe that world’s atmosphere, we can never be sure if it is truly habitable.

Looking for a “true” Earth analog is fraught with challenges. Are we looking for a planet with the same characteristics as modern Earth, or do we try to model our planets during different epochs and work out when Earth life would have been at its most detectable? Life on Earth has been around for the best part of 4 billion years, when would have been best for an alien civilization to detect terrestrial life and what would they have needed to look for?

It’s exactly this question that an international team of researchers is trying to answer.

13 Ways to Hunt Intelligent Aliens

“Clearly what we know about our planet will be our guideline for the characterization of (small rocky worlds in the habitable zones of their stars),” writes the team, headed by Esther Sanroma of the Instituto de Astrofísica de Canarias (IAC), Spain, in a paper accepted for publication in the Astrophysical Journal. “But the Earth has been inhabited for at least 3.8 (billion years), and its appearance has changed with time.”

3 billion years ago, during the Archean eon, the Earth was likely dominated by purple bacteria, a photosynthetic microorganism that inhabited the land and ancient seas. These organisms would have had a very distinctive spectroscopic fingerprint and a tell-tail sign that Earth was covered in a basic form of life.

By modeling different distributions of this microbe throughout the planet — in the oceans, on the land, around coastlines and during different atmospheric conditions — Sanroma’s team used a radiative transfer model “to simulate the visible and near-(infrared) radiation reflected by our planet.” By doing so, they were able to determine that by using multi-color photometric observations, distant observers would be able to “distinguish between an Archean Earth in which purple bacteria inhabit vast extensions of the planet, and a present-day Earth with continents covered by deserts, vegetation or microbial mats.”

ANALYSIS: Purple Plants Might Thrive Under Multiple Stars

When looking for Earth-like worlds, the researchers emphasize the need for exoplanet hunters to be aware that they may not discover a modern-looking Earth-like world, they may stumble across a purple bacteria-dominated world with a very distinctive photometric signature more fitting with an ancient Archean eon Earth-like world.

“Earth is the only planet where life is known to exist; thus observations of our planet will be a key instrument for characterization and the search for life elsewhere. However, even if we discovered a second Earth, it is very unlikely that it would present a stage of evolution similar to the present-day Earth.”

Purple plants may thrive under binary stars.

UNIVERSITY OF ST. ANDREWS

This isn’t the first time that purple alien worlds have been discussed as a possibility. In 2011, researchers examined the exotic energy-generating regimes hypothetical alien plant life would need to develop under sunlight from binary stars.

Over 25 percent of sun-like stars and 50 percent of red dwarf stars exist in binary pairs. Should there be any planets in orbit around binary systems, any life — be it flora or fauna, or some alien form of life that we can’t comprehend, let alone categorize — would be exposed to a broad spectra of light, stretching far into ultraviolet wavelengths. The upshot of this would be purple hued (or even black) plant life that has evolved to optimize photosynthesis.

It seems that in the hunt for extraterrestrial life, all roads lead to purple.

Publication: Characterizing the purple Earth: Modelling the globally-integrated spectral variability of the Archean Earth, E. Sanromá, E. Pallé, M. N. Parenteau, N. Y. Kiang, A. M. Gutiérrez-Navarro, R. López, P. Montañés-Rodríguez, 2013. arXiv:1311.1145 [astro-ph.EP]

Image credit: NASA (purple added)

Indian Mars mission beats neighbours

OPINION: Last Tuesday the Indian space agency launched a mission to Mars. Its goal is to place a satellite into orbit around that planet.

The probe is currently in Earth orbit (although not quite high enough yet, thanks to a brief engine failure yesterday) with a planned insertion into a Mars transfer orbit on December 1. It should reach Mars in September next year.

This is India’s first interplanetary mission. It follows a successful mission to the Moon in 2008-2009.

Why Mars matters

Mars holds a special place in the human mind. In our imaginations we have populated it with intelligent creatures who built canals and pyramids and carved giant faces into the rock. We have had giant worms slither through its sands. We faked an invasion of Earth by Martians.

Enthusiasts amongst us have fantasised about “terraforming” Mars so that we can move there after we have made Earth uninhabitable as a result of our rapacious habits.

The more sober of us see Mars as the most likely site in our solar system for a second origin of life. Discovering even microbes there could revolutionise biology, challenge some religious beliefs and point to an answer to that great question “Are we alone?”.

More prosaically perhaps, “just” getting there can be used to demonstrate the technical expertise of a nation and showcase its industrial ability. Such a “technology demonstrator” is also the first step in developing more ambitious missions.

So the motives for exploring Mars are never likely to be simple. Maybe they don’t matter as long as the results are good. But a number of commentators have noted that if India’s mission is successful they will have stolen a march on Japan and China, in particular.

Japan tried to reach Mars with a launch in 1998 but failed, and China appears to be quickly ramping up its space program. The USA, USSR and Europe got to Mars long ago, first in 1965 with a flyby and then in 1971 with an orbiting mission.

Sniffing for methane

The Indian satellite has scientifically interesting capabilities. One is its ability to detect methane.

This isn’t the first craft to investigate methane. A group using the Planetary Fourier Spectrometer onboard the European Space Agency’s Mars Express spacecraft first reported methane in the planet’s atmosphere in 2004. In a report published in 2009 this appeared to be confirmed by ground-based observations using the Keck telescopes in Hawaii.

Methane is interesting because most of it in our atmosphere is produced by methanogenic Archaea (or microbes); in other words, it is a signal of life. So we might have detected life on Mars.

But like all science it is not so simple.

Methane also comes from volcanic sources. And the ground-based observations could have resulted from methane in our own atmosphere (despite great care in trying to exclude that possibility). More tellingly, the Curiosity rover now active on Mars sniffed and found no methane.

It would be premature to get excited about a detection of life. But a sniff by the Indian instrument could make a useful contribution.

A tiny package, crammed with science

Also included in the instrument package is a photometer that will measure the relative abundance of deuterium and hydrogen in the upper atmosphere. This will allow the amount of water loss to outer space to be estimated, thus revealing an important aspect of the history of water on the planet.

Given that all life as we know it requires liquid water this will be another datapoint in the search for life, as well as revealing more about the climate history of the planet.

A quadrapole mass spectrometer will examine other aspects of the composition of the Martian upper atmosphere.

A thermal infrared imaging spectrometer will measure the properties of the Martian surface, allowing for mapping of surface composition and mineralogy (much of which has already been done by previous missions), and a colour camera will provide images in the visual spectrum.

All this is packed into a cube 1.5 m to a side and powered by solar panels.

There is no doubt that over recent years India has staked a claim to be a serious participant in the exploration of space. More power to them! May they reach Mars, demonstrate their skills and make great discoveries.

Professor Malcolm Walter is director of the Australian Centre for Astrobiology at UNSW.

This article was originally published at The Conversation. Read the original article.

New Evidence for a Martian Ocean

Scientists studying data from NASA's Mars Reconnaissance Orbiter have discovered new evidence that Mars may have once had a vast ocean on its surface. The research team spotted an ancient delta where a river might have emptied into an ocean so large that it covered much of the planet's northern hemisphere.

Delta-like features have been found on Mars before, but most of them appear to flow into craters or similar geological boundaries, and not into places where ocean-sized bodies of water would have been likely to exist. The newly identified delta was found on what would have been the coastline of Mars' ancient ocean, and geological evidence in the delta points toward the ocean's existence.

Mars' northern lowlands have previously been compared to ocean basins on Earth, and scientists have long suspected that this flat area of low elevation is the remnant of an ancient martian seabed. The recent study provides new support for that theory.

The study could also help astrobiologists understand past environments on Mars where surface water persisted for long periods of time. This is important in determining whether or not habitats on ancient Mars were capable of supporting life as we know it.

The study, "Deltaic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars," was published in the July 12 issue of the Journal of Geophysical Research

The Day the Earth Smiled ( credits: Jet Propulsion Laboratory )

Figure 1

Figure 2	Figure 3

On July 19, 2013, in an event celebrated the world over, NASA's Cassini spacecraft slipped into Saturn's shadow and turned to image the planet, seven of its moons, its inner rings -- and, in the background, our home planet, Earth.

With the sun's powerful and potentially damaging rays eclipsed by Saturn itself, Cassini's onboard cameras were able to take advantage of this unique viewing geometry. They acquired a panoramic mosaic of the Saturn system that allows scientists to see details in the rings and throughout the system as they are backlit by the sun. This mosaic is special as it marks the third time our home planet was imaged from the outer solar system; the second time it was imaged by Cassini from Saturn's orbit; and the first time ever that inhabitants of Earth were made aware in advance that their photo would be taken from such a great distance.

With both Cassini's wide-angle and narrow-angle cameras aimed at Saturn, Cassini was able to capture 323 images in just over four hours. This final mosaic uses 141 of those wide-angle images. Images taken using the red, green and blue spectral filters of the wide-angle camera were combined and mosaicked together to create this natural-color view. A brightened version with contrast and color enhanced (Figure 1), a version with just the planets annotated (Figure 2), and an annotated version (Figure 3) are shown above.

This image spans about 404,880 miles (651,591 kilometers) across.

The outermost ring shown here is Saturn's E ring, the core of which is situated about 149,000 miles (240,000 kilometers) from Saturn. The geysers erupting from the south polar terrain of the moon Enceladus supply the fine icy particles that comprise the E ring; diffraction by sunlight gives the ring its blue color. Enceladus (313 miles, or 504 kilometers, across) and the extended plume formed by its jets are visible, embedded in the E ring on the left side of the mosaic.

At the 12 o'clock position and a bit inward from the E ring lies the barely discernible ring created by the tiny, Cassini-discovered moon, Pallene (3 miles, or 4 kilometers, across). (For more on structures like Pallene's ring, seePIA08328). The next narrow and easily seen ring inward is the G ring. Interior to the G ring, near the 11 o'clock position, one can barely see the more diffuse ring created by the co-orbital moons, Janus (111 miles, or 179 kilometers, across) and Epimetheus (70 miles, or 113 kilometers, across). Farther inward, we see the very bright F ring closely encircling the main rings of Saturn.

Following the outermost E ring counter-clockwise from Enceladus, the moon Tethys (662 miles, or 1,066 kilometers, across) appears as a large yellow orb just outside of the E ring. Tethys is positioned on the illuminated side of Saturn; its icy surface is shining brightly from yellow sunlight reflected by Saturn. Continuing to about the 2 o'clock position is a dark pixel just outside of the G ring; this dark pixel is Saturn's Death Star moon, Mimas (246 miles, or 396 kilometers, across). Mimas appears, upon close inspection, as a very thin crescent because Cassini is looking mostly at its non-illuminated face.

The moons Prometheus, Pandora, Janus and Epimetheus are also visible in the mosaic near Saturn's bright narrow F ring. Prometheus (53 miles, or 86 kilometers, across) is visible as a faint black dot just inside the F ring and at the 9 o'clock position. On the opposite side of the rings, just outside the F ring, Pandora (50 miles, or 81 kilometers, across) can be seen as a bright white dot. Pandora and Prometheus are shepherd moons and gravitational interactions between the ring and the moons keep the F ring narrowly confined. At the 11 o'clock position in between the F ring and the G ring, Janus (111 miles, or 179 kilometers, across) appears as a faint black dot. Janus and Prometheus are dark for the same reason Mimas is mostly dark: we are looking at their non-illuminated sides in this mosaic. Midway between the F ring and the G ring, at about the 8 o'clock position, is a single bright pixel, Epimetheus. Looking more closely at Enceladus, Mimas and Tethys, especially in the brightened version of the mosaic, one can see these moons casting shadows through the E ring like a telephone pole might cast a shadow through a fog.

In the non-brightened version of the mosaic, one can see bright clumps of ring material orbiting within the Encke gap near the outer edge of the main rings and immediately to the lower left of the globe of Saturn. Also, in the dark B ring within the main rings, at the 9 o'clock position, one can see the faint outlines of two spoke features, first sighted by NASA's Voyager spacecraft in the early 1980s and extensively studied by Cassini.

Finally, in the lower right of the mosaic, in between the bright blue E ring and the faint but defined G ring, is the pale blue dot of our planet, Earth. Look closely and you can see the moon protruding from the Earth's lower right. (For a higher resolution view of the Earth and moon taken during this campaign, see PIA14949.) Earth's twin, Venus, appears as a bright white dot in the upper left quadrant of the mosaic, also between the G and E rings. Mars also appears as a faint red dot embedded in the outer edge of the E ring, above and to the left of Venus.

For ease of visibility, Earth, Venus, Mars, Enceladus, Epimetheus and Pandora were all brightened by a factor of eight and a half relative to Saturn. Tethys was brightened by a factor of four. In total, 809 background stars are visible and were brightened by a factor ranging from six, for the brightest stars, to 16, for the faintest. The faint outer rings (from the G ring to the E ring) were also brightened relative to the already bright main rings by factors ranging from two to eight, with the lower-phase-angle (and therefore fainter) regions of these rings brightened the most. The brightened version of the mosaic was further brightened and contrast-enhanced all over to accommodate print applications and a wide range of computer-screen viewing conditions.

Some ring features -- such as full rings traced out by tiny moons -- do not appear in this version of the mosaic because they require extreme computer enhancement, which would adversely affect the rest of the mosaic. This version was processed for balance and beauty.

This view looks toward the unlit side of the rings from about 17 degrees below the ring plane. Cassini was approximately 746,000 miles (1.2 million kilometers) from Saturn when the images in this mosaic were taken. Image scale on Saturn is about 45 miles (72 kilometers) per pixel.

This mosaic was made from pictures taken over a span of more than four hours while the planets, moons and stars were all moving relative to Cassini. Thus, due to spacecraft motion, these objects in the locations shown here were not in these specific places over the entire duration of the imaging campaign. Note also that Venus appears far from Earth, as does Mars, because they were on the opposite side of the sun from Earth.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://www.nasa.gov/cassini andhttp://saturn.jpl.nasa.gov.