But this time it wasn't their distance from HR8799 that enabled the researchers to spot them. It was their youth. They are only about 60 million years old. Researchers realized young planets would still be glowing from their formation, generating enough heat to be seen in the infrared spectrum.
"Seeing these planets directly -- separating their light from the star -- lets us study them as individuals, and use spectroscopy to study their properties, like temperature or composition," said MacIntosh.
It appears all three planets have complex atmospheres, with dusty clouds that trap radiating heat, scientists said.
Not everyone was ready to pop champagne corks. Alan Boss, a physicist with the Carnegie Institution in Washington, said he still needed more evidence to be convinced. "Only time will tell," he said.
European planet-hunters using the Very Large Telescope in Chile made claims a couple of years ago that they had imaged exoplanets, but those claims were disputed by scientists who believed the planets were actually brown dwarfs.
The twin discoveries mean researchers have found alien planets whose orbits are close to (seen using the wobble technique) and far away from (via direct imaging studies) stars outside our solar system. That still leaves a vast area in between, where any Earth-like planets are likely to reside.
Probing that territory awaits at least one leap forward in technology. The first is a new and improved adaptive optics system called the Gemini Planet Imager. Expected to be 100 times more sensitive than current instruments, it should be able to find planets the size of Jupiter around other stars.
It is expected to be in operation on the Gemini South telescope in Chile in 2011.
HR8799 will be a key target.
"I think there's a very high probability that there are more planets in the system that we can't detect yet," MacIntosh said.
Finding the next Earth could require a leap beyond that, perhaps with a space mission such as the Terrestrial Planet Finder. Proposed by NASA several years ago, it would include a suite of space-based observatories outfitted to search for Earth-like planets in our neighborhood of space.
That mission has been deferred for budgetary reasons.
--
john.johnson@latimes.com
