Earth's cloudy past could reveal exoplanet details

Jan 24, 2012 By Nola Taylor Redd
Earth’s clouds as seen from the space shuttle. Clouds cluster over vegetative landforms and along ocean currents, reflecting light from the Sun into space. Credit: NASA Johnson Space Center Collection

The pattern of clouds on Earth is largely determined by the arrangement of the continents below. Now, astronomers are modeling the clouds at different periods in Earth's past to better understand what alien worlds might look like.

Two astronomers from Spain are trying to determine how brightly would shine in the age of the dinosaurs. Their results not only reveal how Earth would look to a distant observer, but could also help astronomers determine the layout of landforms on faraway planets.

Rather than relying on , the pair analyzed the relationship between cloud cover and landforms to calculate how clouds would gather over different regions.

“When you look at the planet...it has a given distribution of continents and clouds,” said Enric Palle, of the Astrophysical Institute of the Canary Islands (IAC).

“But it has not always been the same.”

With the relationship in hand, they looked back in time to measure how much the brightness of the planet would vary as the continents of Earth shifted 90, 230, 340, and 500 million years ago, when the planet had a different layout.

Studying the changes in the light reflected from the Sun (the albedo) could help astronomers figure out what might lay under the clouds of extrasolar planets.

When life tries to hide

Palle and lead author Esther Sanroma, also of the IAC, used 23 years worth of data on the global distribution of clouds over various landforms from the International Satellite Cloud Climatology Project. Detailed landform models from paleogeologist Ron Blakely provided them with a layout of the Earth over four different time periods.

They wanted to look farther back, but the atmosphere has only had a similar temperature and composition for the last half billion years.

They found that for much of Earth’s history, the daily variations were minimal. Such small shifts would be a challenge to measure from a distance.

However, 500 million years ago, there were huge swings in the light as the planet rotated each day. The variations were four times as large as changes in other periods.

The authors attribute this to two causes.

First, the land masses were closer together, rather than spread out, leaving wider expanses of oceans. These result in a wildly different cloud distribution.

The Earth’s continents 85 million years ago. The different continental distribution would have influenced cloud cover.

Second, the land half a billion years ago was all desert, completely bare of all life.

”Five hundred million years ago is the time in which life evolved from oceans to land,” Palle said.

As plants began to cover the land, the cloud arrangement shifted. Deserts have few clouds, because there is very little water vapor in the air. Thus, the advent of life brought changes that would have made Earth more difficult to examine from space.

“We camouflaged ourselves, and made it more difficult for a distant observer to characterize the Earth,” Palle said.

The process could work in reverse - a light curve with small changes could potentially indicate vegetation on another planet.

Of course, astronomers studying an exoplanet would need more information before they could definitively reach such a conclusion.

In December, astronomers announced the discovery of Kepler-22b, the first planet in the habitable zone of a sun-like star. Though its gas envelope raises the temperature too high for liquid water on the surface, other rocky planets within similar distances from their star could potentially boast water and clouds. Image credit: NASA/Ames/JPL-Caltech

The link between land and clouds

Watching your local weather, it might seem as though the movement and behavior of clouds are random, but in fact they are not. Wider trends emerge when you look at the planet on a global scale.

“There are some spots on Earth that are always cloudy, like over the Amazon rainforest, and there’s other spots like the Sahara desert which are always clear,” said planetary scientist Sara Seager, of the Massachusetts Institute of Technology. Seager, who was not involved in this research, models the atmospheres of exoplanets.

Rather than relying on climate modeling to predict how clouds would behave, Palle and Sanroma decided to take advantage of these trends.

Their model assumes that such patterns would continue in the past, with clouds behaving the same way over oceans and deserts as they do today.

“Big cloud patterns, on a global scale, are tied to the continental distribution and ocean circulation,” Palle said.

By applying this pattern to other time frames, they were able to calculate how widely the brightness of Earth would change over the course of its daily rotation.

“This is a different way of looking at the problem,” Seager said.

According to Palle, a new approach was necessary to look so far back in time.

He points out that we have about 30 global models predicting the cloud formation in a hundred years in the future. Though they agree that the temperature will change in response to an increase in carbon dioxide, they provide a range of responses to how the clouds will react - and no one knows which one might be correct.

By focusing on the patterns of clouds over land and ocean, Sanroma and Palle hope to overcome the uncertainties that crop up in climate modeling.

Artist’s depiction of the Terrestrial Planet Finder (TPF) chronograph and inferometer, each which could have studied exoplanets. Credit: NASA

The search for planets

So how long before we can identify the of distant planets?

“It might be feasible with the next generation of space telescopes,” Palle said.

At the present, nothing is planned that would be able to detect such variations, but perhaps in the near future.

“The TPF (Terrestrial Planet Finder) would have been able to take this kind of observations for a close planet,” he said.

NASA’s Terrestrial Planet Finder, or TPF, had a proposed goal of studying all aspects of exoplanets, but, after being proposed several times, it was canceled in 2011.

”We hope that our TPF concept will be resurrected and will launch sometime in the future,” Seager said.

As astronomers study extrasolar planets, they can determine much of its composition from the changes in brightness. Rocky planets with no atmosphere, icy planets, and planets with permanent cloud cover would all have almost no variations.

But, according to Palle, “if it has an atmosphere with broken clouds, we will see it in variability.”

The scattered would imply oceans on the surface, which could be potential habitats for the development of life. The type of liquid would depend on how close the planet lay to its sun.

“If it has water , it has water oceans,” Seager said.

Palle agrees.

“Any water raining down will eventually create an ocean. Maybe smaller than we have on Earth, but still, an ocean.”

Explore further: ITAR-TASS claims Russian cosmonauts have found sea plankton on outside of International Space Station

Related Stories

Update on Gliese 581d's habitability

May 09, 2011

When last we checked in on Gliese 581d, a team from the University of Paris had suggested that the popular exoplanet, Gliese 581d may be habitable. This super-Earth found itself just on the edge of the Gold ...

HARPS tunes in on habitable planet

Sep 05, 2011

Using the High Accuracy Radial velocity Planet Searcher (HARPS), a team of scientists at University of Geneva, Switzerland, led by the Swiss astronomer Stephane Udry made a sound discovery… an Earth-like ...

Stellar eclipse gives glimpse of exoplanet

Jul 19, 2011

A group of astronomers led by an MIT professor has spotted an exoplanetary eclipse of a star only 40 light years away — right around the corner, astronomically speaking — revealing a "super-Earth."

Setting sight on a single star

May 16, 2011

NASA recently selected 20 small satellites to fly as auxiliary cargo aboard rockets that are planned to launch in 2011 and 2012.

Coming to a solar system near you… super-Earth!

Aug 08, 2011

It is our general understanding of solar system composition that planets fall into two categories: gas giants like Jupiter, Saturn, Neptune and Uranus… and rocky bodies that support some type of atmosphere ...

Seeing the planets for the trees

May 20, 2011

A recent study says that a particular mathematical technique could be used to detect forests on extrasolar planets.

Recommended for you

NKorea launch pad expansion 'nearing completion'

11 hours ago

A U.S. research institute says construction to upgrade North Korea's main rocket launch pad should be completed by fall, allowing Pyongyang (pyuhng-yahng) to conduct a launch by year's end if it decides to do so.

Mars, Saturn and the claws of Scorpius

17 hours ago

Look up at the night sky this week and you'll find Mars and Saturn together in the west. Mars stands out with its reddish colouring and you might just be able to detect a faint yellow tinge to Saturn. ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

Graeme
not rated yet Jan 24, 2012
The method using stellar transits should also be able to detect clouds if more light can be collected from the star. Variable clouds should show up in slight changes to when the light from the star was dimmed as the planet started crossing the stellar disk. Clouds around the edge of the planet disk would cast their shadow on earth, but during the transit we would only notice an average over the whole circle.
kevinrtrs
1 / 5 (2) Jan 25, 2012
The main problem with this research is this incredible ability:
they looked back in time

With this, it basically comes down to speculation based on questionable assumptions. No matter which camp you come from, the resultant lack of credibility should be obvious.
aroc91
not rated yet Jan 25, 2012
The main problem with this research is this incredible ability:
they looked back in time

With this, it basically comes down to speculation based on questionable assumptions. No matter which camp you come from, the resultant lack of credibility should be obvious.


We know the concepts behind cloud formation. They follow patterns. It's not difficult to apply it a different topography.
Jorsher
5 / 5 (1) Jan 27, 2012
I prefer using modern evidence to guess past events over using old books without any modern evidence to assume past events.