A Drop in the Bucket

February 18, 2010 by Anuradha K. Herath
A reddish jet of gas emanates from the forming star HH-30, which is surrounded by a protoplanetary disk. Credit: NASA/ESA

A new technique is being developed to detect water in the protoplanetary disks of other solar systems. If successful, it would help in our understanding of how habitable planets form.

The search for on other planetary bodies has taken a giant leap forward in recent months. In November, NASA announced that it had found substantial quantities of water on the Moon. Earlier this month, the obtained data about one of Saturn’s moons, Enceladus, that may confirm the presence of sub-surface liquid water.

While these missions scour our solar system for traces of water - a necessary condition for life - a group of scientists is looking beyond, at solar systems light years away. A recent study published in the journal Astrobiology described using infrared spectroscopy to model the dust surrounding young extrasolar stars to try to detect the presence of hydrous minerals called phyllosilicates.

One of the simplest examples of phyllosilicates is clay minerals. Water is an important part of their chemical structure.

“If you find phyllosilicates, you have most likely found liquid water,” says lead author Melissa Morris, a visiting professor in the Department of Physics, Astronomy and Materials Science at Missouri State University and an affiliate of Arizona State University’s School of Earth and Space Exploration. “The objective was to try to determine whether we could actually detect these wonderful signatures of hydrated minerals almost always produced by the interaction of liquid water with rock.”

In order to determine whether the surface of an extrasolar planet would contain water, scientists can look at what is called the protoplanetary disk - a disk of gas and dust surrounding a star during its early stages of development. Scientists think planets are born from protoplanetary disks through gravitational and electrostatic interactions between particles. So if scientists can determine the elemental composition of the dusty disks that orbit young stars, they should be able to predict what sort of planets will eventually form.

One school of thought suggests that the Earth acquired its surface water from asteroids or asteroid-like bodies that were present in its protoplanetary disk. The authors of this study used the same assumption for potential Earth-like planets in other solar systems. Therefore, if phyllosilicates are found in the protoplanetary disk of a young extrasolar star, the assumption is that water would most likely be found on the surface of planets that are later born within the disk. (Of course, as Mercury, Venus and Mars illustrate, other conditions will affect whether a rocky planet ultimately has water.)

The scientists hope to someday use instruments such as the Spitzer Space Telescope and the Stratospheric Observatory for Infrared Astronomy (SOFIA) to determine the composition of exozodiacal dust in extrasolar protoplanetary disks. Before that can be done, however, scientists must first determine if detection of particular minerals in these distant systems is even possible. This study helps scientists determine what signatures to look for in disks.

The composition of the dust is identified by studying its emission features. A common procedure is to use to identify substances by the infrared wavelengths they absorb or emit. This procedure is often used to detect water on planetary bodies.

A picture taken by the Hubble Space Telescope showing an edge-on view of a protoplanetary disk around a newborn star in the Orion Nebula, located 1,500 light-years away. Credit: Mark McCaughrean (Max-Planck-Institute for Astronomy), C. Robert O'Dell (Rice University) and NASA

Morris and her colleagues began by modeling the infrared emission features of dust that did not contain hydrated minerals, or phyllosilicates. They then changed the mineral mixture by adding phyllosilicates amounting to three percent of the total mixture.

In the paper, Morris and her co-author Steve Desch of Arizona State University claim that unique features indicative of phyllosilicates in the mid-infrared spectra should make it possible to detect those minerals in protoplanetary disks.

Scott Sandford, a research astrophysicist at the NASA Ames Research Center in California who has experience conducting spectroscopy in meteorites, thinks that proving the presence of phyllosilicates in a protoplanetary disk could be a challenge. It would be an especially difficult task if phyllosilicates only make up a small portion of the disk material, or if a variety of phyllosilicate minerals are present.

“It is somewhat difficult to identify phyllosilicates when they are present in mixtures because they are relatively featureless as opposed to other minerals, which have a lot of structural features in their spectrum,” says Sandford.

Morris says the outcome of this study shows only that, based on the computer models, it should be possible to detect the presence of phyllosilicates in protoplanetary disks. It is only the first step in the detection of water in other solar systems.

“My part was developing the model to determine whether it could be done,” says Morris. “What instruments are available? Of the instruments we have, do they have the resolution?”

This plot of infrared data, captured by the Spitzer Space Telescope, shows the signatures of water vapor and simple organic molecules in the disk of gas and dust surrounding a young star. Credit: NASA/JPL-Caltech/J. Carr (Naval Research Laboratory)

The next step, which Morris has already begun, is to apply this technique to actual data. Morris is now comparing the models to data obtained from the Spitzer Space Telescope.

Sandford says that will be the real test.

“The basic idea they are espousing is a perfectly good one,” says Sandford. “I'm personally kind of skeptical that you can locate the phyllosilicates in disks to the level they suggest. How applicable are those models to the real world? In any event, the only way to find out is to try -- and they have done the intial ground work to do that.”

Morris says this type of research is also important in understanding how planetary systems form in general.

“I’m a huge advocate for looking for water in our own solar system,” says Morris, “but just to understand the process of planetary system formation, we need to go outside our and look at other systems as well.”

Explore further: Water Vapor Detected in Protoplanetary Disks

Related Stories

Water Vapor Detected in Protoplanetary Disks

March 19, 2008

Water is an essential ingredient for forming planets, yet has remained hidden from scientists searching for it in protoplanetary systems, the spinning disks of particles surrounding newly formed stars where planets are born. ...

Ideas on gas-giant planet formation take shape

March 22, 2006

Rocky planets such as Earth and Mars are born when small particles smash together to form larger, planet-sized clusters in a planet-forming disk, but researchers are less sure about how gas-giant planets such as Jupiter and ...

Baby Jupiters must gain weight fast

January 5, 2009

The planet Jupiter gained weight in a hurry during its infancy. It had to, since the material from which it formed probably disappeared in just a few million years, according to a new study of planet formation around young ...

First Direct Imaging of a Young Binary System

December 15, 2009

(PhysOrg.com) -- A team of astronomers from The Graduate University for Advanced Studies, the National Astronomical Observatory of Japan, and other universities have captured the first direct image of a young binary star ...

Recommended for you

New eruptions detected in two luminous blue variables

December 12, 2017

(Phys.org)—Astronomers report the detection of new eruptions in two luminous blue variables, known as R 40 and R 110, located in the Magellanic Clouds. The finding, presented December 5 in a paper published on the arXiv ...

Juno probes the depths of Jupiter's great red spot

December 12, 2017

Data collected by NASA's Juno spacecraft during its first pass over Jupiter's Great Red Spot in July 2017 indicate that this iconic feature penetrates well below the clouds. Other revelations from the mission include that ...

Telescopes team up to study giant galaxy

December 12, 2017

Astronomers have used two Australian radio telescopes and several optical telescopes to study complex mechanisms that are fuelling jets of material blasting away from a black hole 55 million times more massive than the Sun.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.