When Vincent van Gogh touched paint brush to canvas, he probably didn’t know that 41 light years away, five planets orbit around 55 Cancri, a star in the constellation Cancer. When he swirled together the blues, whites, yellows and oranges, he probably didn’t know he might be painting a star that, for other life forms, is a sun.

And when he took a step back and looked at his finished “The Starry Night,” he probably didn’t know he was looking at one of our solar system’s closest relatives.

In fact, even astronomers didn’t know about the fifth planet — which, though it was discovered last, is the fourth planet from 55 Cancri — until early November. By this time, the village in van Gogh’s “Starry Night” had been sitting beneath those painted stars for more than a century.

The discovery, which named 55 Cancri the largest extrasolar planetary system in the Milky Way, is just one step further in the discovery of more and larger planetary systems, according to Robert Egler, a senior astronomy lecturer.

“When I first started in astronomy, the big talk was that we thought most stars have planets, but no one had ever seen one,” he said. “Then in 1995 we discovered the first planet orbiting a star. Now, we’ve discovered more than 250. It won’t be too long before we start finding Earth-sized planets around stars.”

Finding invisible planetsAlthough many people tend to imagine the sun remaining stationary as eight planets (and an ousted Pluto) continue their orbits, Egler said the sun actually moves slightly as the planets travel. For each planet, the sun maintains a distinct gravatational wobble.

Astronomers use this gravitational wobble — caused by a star’s planets — to detect orbiting planets, Egler said. So while scientists cannot directly see or take satellite images of the orbiting planets, they can locate a planet and estimate its size and mass by other means.

The same is true for the Earth and the moon, Egler said.

“It’s not that the Earth is sitting here and the moon is going around it,” he said. “If you could watch the Earth and not see the moon, you would still see the Earth wobble very slightly.”

When astronomers look at an individual star, they analyze its wobble. From there, they deduce what other objects have to be orbiting around it to cause this particular movement.

However, Egler said it has been only during recent years that astronomers have been able to use technologies that detect smaller planets.

“The techniques are now at the point where we can see relatively small planets at resonable distances [from a satellite]. We used to only be able to detect large planets located close to stars because they cause a bigger wobble in the star, so we can see it easier,” he said. “As technology improves, we can see smaller and smaller wobbles.”

A second Earth?As astronomers search the skies, Egler said they are seeking the “holy grail”: an Earth-sized planet that lies in the star’s “habitable zone.” Planets that fit this description are capable of sustaining life.

“This system has five planets which lie in the habitable zone. They’re close enough to 55 Cancri that they’re warm enough to have life, but not so far that they’d be too cold to sustain it,” he said. “Venus, Mars and Earth lie in the habitable zone in our system, but only one planet has life.

“Mercury is way too hot. Jupiter is warm enough, but it’s huge and it doesn’t have a solid surface,” Egler said. “We need to find a planet that doesn’t have a molten surface, but also one that’s not frozen at all times.”

And the fifth planet lies within these boundaries.

Although Egler said the planet is about 45 times the size of Earth, it’s relatively small in comparison to some of the other planets astronomers have found — some of which can surpass Jupiter’s size 10 times over. And with an orbit like Venus’ — 260 days — the planet holds more potential than many others.

“The biggest thing is that this is now the solar system we know of that has the most planets, other than our own,” Eglers said. “It’s possible that you could have some sort of life on this planet. It’s the first planet that you could really look at, outside of the solar system, and say, ‘It’s about right, it has the possibility for life.’ The big thing is that it’s the right distance from its star.”

Playing the numbers gameWith the discovery of this familiar-looking planet, astronomers have taken new strides toward potentially discovering extraterrestrial life forms, according to Christopher Brown, director of the N.C. Space Initiative.

“The importance of this is, in our quest to understand our place in the solar system and in the Universe, that this might be another place where life exists,” said Brown, who is also the associate vice chancellor for research development and professor of plant biology. “Life is probably not going to exist on a star, but it could exist on a planet where conditions are relatively milder. That’s the exciting part of it.”

Though astronomers have introduced theories that name Mars and some of Jupiter’s moons’ potential homes for life, Brown said the numbers game comes into play when they consider the idea that there are “other planets around other stars in other galaxies.”

“As far as planets are concerned, we know our own solar system and really no others,” he said. “There are billions and billions of other stars … where there are other living things in the Universe besides that which we find on Earth.”

‘Microbes or space dolphins’It isn’t likely that while combing extrasolar planets for evidence of life, astronomers will find power-hungry, intelligent beings, Brown said. These types of science fiction extraterrestrials are neither what astronomers hope or expect to find.

“I don’t think that we need to worry about intelligent beings coming in and sucking all the life out of Earth,” he said. “I don’t feel that there’s a good possibility of that because life is very competitive and there’s plenty of things living here on the Earth. They wouldn’t be able to take over everything.”

A more realistic concern, he said, would be forward contamination — contaminating another planet with bacteria or microorganisms — which would make it harder to discern the planet’s existing life from Earth life. Brown said reverse contaminiation is another worry.

“Reverse contamination is [a situation in which] some life form from another planet comes here and can run rampant — potentially,” he said.

But since no life forms have been discovered, Egler said he has no idea what to expect. The search for life continues through finding planets capable of sustaining life.

“It could have microbes or space dolphins for all I know,” Egler said.

Keeping an open mindBecause so much of the solar system remains mysterious, Brown said it is important to keep searching for life on Mars. The key isn’t finding life on extrasolar planets, but searching for existing or extinct life on a planet that’s not so far away from Earth.

“That’s the question to be answered first,” he said. “I’m confident that they will eventually discover that there was life on Mars in the past — and probably still is.”

There are two steps that must be taken, Brown said, if life is found on other planets.

“Scientifically we deal with it very carefully. We need to protect Mars as much as possible and keep it a pristine site for study. We don’t want to carry anything up there on the spacecraft and then contaminate the planet,” he said. “As for dealing with it socially, I’ll leave that to others. It’s important for us to be open-minded to the fact that we may not be the only place where there is life.”