Finding planets around other stars is tricky enough, but actually getting images of them is all but impossible. That’s why Centauri Dreams has been so fascinated with the starshade concept, and with one particular design for it, called (depending on the mission) New Worlds Discoverer, New Worlds Observer or New Worlds Imager. We saw recently that Webster Cash (University of Colorado at Boulder) had been pitching NASA to do a concept study on New Worlds for a Discovery-class mission, but the proposal didn’t make the cut, in this round at least.
That’s disappointing, but as Cash told me in an interview earlier this year, “If we don’t win this one, we’ll win the next one.” There is reason for such optimism because the New Worlds mission designs offer many of the benefits of the Terrestrial Planet Finder mission once slated for this kind of work at a fraction of the cost, and as I mentioned earlier this week, New Worlds has the potential of working with the James Webb Space Telescope to uncover vistas never before seen, studying up to 100 stars in three years and examining the habitable zones of almost all of them.
Starshades are objects that block light, and if the world worked solely according to our senses, it would seem that putting an object directly in front of a star to mask its light should allow us to see the planets around it. But there’s a flaw in the plan: light waves diffract, bending around whatever object we use to mask the star’s light. Get right behind a disc-shaped space-based occulter and you would see a bright ring around its edge as light waves bend around the occulter, their interference sharply reducing the effectiveness of the device.
Cash’s work involves a disk with petal-shaped additions, the idea being to offset the path length of the light waves enough that the rays cancel each other out. The result is to create a shadow behind the occulter within which a telescope can be flown, and one intense enough to allow the faint lights of planets to be seen despite the star’s glare. Cash is building a New Worlds Web site to illustrate these concepts — thanks to Ian Jordan (Space Telescope Science Institute) for a heads-up on the new site’s creation.
Image: A New Worlds-class starshade. By adding petals onto the disc’s edge, the path length of each ray of light is offset just enough so that the combined effect is destructive interference and the creation of deep shadow. Credit: Webster Cash, Eric Schindhelm.
You can see an animation of the concept here, but be aware that the New Worlds site is just getting launched. As design and planning goes on for future mission proposals, you might also keep an eye on UMBRAS (Umbral Missions Blocking Radiating Astronomical Sources), whose site offers background information on starshades, their design and uses. Some of the people involved with UMBRAS are working with Cash on the New Worlds studies, so either site may become a source for more news.
very interesting. but the other day in the astronomy magazine collectors edition i bought as part of my subscription i read that planets,or at least one,have been found as far off as another galaxy! question space fans – a globular star cluter is another galaxy?…right. but the point was made that this place was so old that “they could have been building starships when life on earth was just beginning! really fires the imagination regarding the possibility of intelligent life elsewhere. thank you, george scaglione
George, I think the planet the magazine was referring to was one of the ones found through gravitational microlensing in the direction of the Milky Way’s center. I haven’t heard of anything detected as far away as another galaxy.
Re your question, though, globular clusters are not independent galaxies, but rather ancient formations that orbit the galactic core. They’re common around galaxies, and the Milky Way seems to have around 150 of them. The Wikipedia has a good article about globular clusters:
http://en.wikipedia.org/wiki/Globular_cluster
And yes, bear in mind that many stars are far older than our own. Even the nearest stars to Earth, Centauri A and B and Proxima Centauri, are substantially older — if evolution ever started around one of these stars, life there has had a major jump on us!
yes, thank you.i’m afraid i just got excited and went off half cocked i took another look and found “the ancient world lies 7,200 light years away in globular cluster m4 in the constellation scorpius”but if i don’t get excited about this stuff lol then what should i become excited about!? also i read that carl sagan felt that there could be up to 1,000,000 technological species in our galaxy.but for now i better quit while i’m ahead and leave that for another day. thanks yet again your friend george
One trillion minisats to shade Earth and stop global warming?
University of Arizona, 3 November 2006
http://uanews.org/cgi-bin/WebObjects/UANews.woa/wa/MainStoryDetails?ArticleID=13269
To quote:
Researchers have proposed various alternatives for cooling the planet, including
aerosol scatterers in the Earth’s atmosphere. The idea for a space shade at L1
to deflect sunlight from Earth was first proposed by James Early of the Lawrence
Livermore National Laboratory in 1989.
“The earlier ideas were for bigger, heavier structures that would have needed
manufacture and launch from the moon, which is pretty futuristic,” Angel said.
“I wanted to make the sunshade from small ‘flyers,’ small, light and extremely
thin spacecraft that could be completely assembled and launched from Earth, in
stacks of a million at a time. When they reached L1, they would be dealt off the
stack into a cloud. There’s nothing to assemble in space.”
I say we take those trillion satellites, put a few sensors on them,
and send them out into the Milky Way galaxy. And don’t forget
the micro info packets to explain to the finders who made them
and where they came from!
As has been reported here earlier, even a very simple probe
could reveal much about other star systems:
https://centauri-dreams.org/?p=733
A few big probes (Daedalus) covering a few star systems is
not going to cut it if we want to find extraterrestrial life in
the short term. That’s why so many plants spread millions
of seeds and spores in the hopes of carrying on their DNA,
to improve the chances of success.
Does the same calculation apply to the shape of the objective lens on a telescope? i.e. can we increase resolution / contrast of an image by placing a shaped mask round the edge of the mirror / lens on a telescope?
Reference above administrator’s link to Wiki for globular clusters, I just followed and read the article, it is GOOD! Much thought provoking material.
USA Today article on the Starshade:
http://www.usatoday.com/tech/science/columnist/vergano/2007-02-04-starshade_x.htm
MIT, others ask ‘What would E.T. see?’
Team analyzes how alien astronomers would study Earth
======================================
For Immediate Release
THURSDAY, DEC. 20, 2007
Contact: Patti Richards,
MIT News Office
Phone: 617-253-8923
Email: prichards@mit.edu
PHOTOS AVAILABLE
CAMBRIDGE, Mass – As astronomers become more adept at searching for, and
finding, planets orbiting other stars, it’s natural to wonder if anybody
is looking back. Now, a team of astronomers that includes a professor from
MIT has figured out just what those alien eyes might see using technologies
being developed by Earth’s astronomers.
According to their analysis, among other things E.T. could probably tell that
our planet’s surface is divided between oceans and continents, and learn a
little bit about the dynamics of our weather systems.
“Maybe somebody’s looking at us right now, finding out what our rotation
rate is – that is, the length of our day,” says Sara Seager, associate
professor of physics and the Ellen Swallow Richards Associate Professor of
Planetary Sciences at MIT.
Seager, along with Enric Palle and colleagues at the Instituto Astrofisica del
Canarias, in Spain, and Eric Ford (MIT class of 1999) of the University of
Florida, have done a detailed analysis of what astronomers here and on other
worlds could learn about a planet from very distant observations, using
telescopes much more powerful than those currently available to Earth’s
astronomers. Their study, which has just been published online in the
Astrophysical Journal, will appear in the journal’s print edition in April.
Most of the planets astronomers have discovered beyond the Solar System have
not actually been seen; rather, they have been indirectly observed by looking
at the influence they exert on stars they orbit. But even with the most
advanced telescopes planned by Earth’s astronomers for use over the next
several years, a planet orbiting another star would only appear as a single
pixel-that is, a single point of light, with no detail except its brightness
and color. By comparison, a simple cellphone camera typically takes pictures
with about a million pixels, or one megapixel.
“The goal of [our] project was to see how much information you can extract”
from very limited data, Seager says. The team’s conclusion: a great deal of
information about a planet can be gleaned from that single pixel and the way
it changes over time.
The way of analyzing the data that Seager and her co-authors studied would
work for any world that has continents and bodies of liquid on its surface
plus clouds in its atmosphere, even if those were made of very different
materials on an alien world. For example, icy worlds with seas of liquid
methane, like Saturn’s moon Titan, or very hot worlds with oceans of molten
silicate (which is solid rock on Earth), would show up similarly across the
vastness of space.
However, the method depends on clouds covering only part of a planet’s surface,
regardless of what each world is made of. So Titan, covered by perpetual
global smog, would not give up the mysteries of its weather or rotation,
nor would the hellishly hot Venus, with its complete shroud of clouds.
The key, the astronomers learned after sudying data from Earth’s weather
satellites, is that while clouds vary from day to day, there are overall
patterns that stay relatively constant, associated with where arid or rainy
landmasses are. Detecting those repeating patterns would allow distant
astronomers to figure out the planet’s rotation period because a brightening
associated with clouds above a particular continent would show up regularly
once each “day,” whatever the length of that day might be. Once the day’s
length is determined, then any variations in that period would reveal the
changing weather-that is, clouds in a different place than the average.
No telescope now in operation is capable of making the measurements that
Seager and her team analyzed. But planned telescopes such as NASA’s Kepler,
set for launch in 2009, would be able to discover dozens or hundreds of
Earth-like worlds. Then even more advanced space observatories being
considered, such as NASA’s Terrestrial Planet Finder, would allow the
followup studies to learn about these planets’ rotation and weather, and
the composition of their atmospheres, Seager says.
The research was funded in part by a Ramon y Cajal fellowship for Palle,
and a Hubble Fellowship grant for Ford and by NASA.