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{Artwork shows the Jupiter-scale planet in orbit around a double-star

system that includes a pulsar, near the lower edge of the frame.)

 

Oldest known world boggles minds

Could alien life have begun earlier than scientists thought?

 

By Robert Roy Britt

SPACE.COM

 

July 10 — Astronomers have discovered the oldest known planet,

a primeval world 12.7 billion years old that will force them to

reconsider how and when planets form. The discovery raises the

prospect that life may have begun far sooner than most scientists

ever imagined. A leading planet-formation expert not involved in the

work called the discovery mind-boggling.

 

 

AN EARLY EARTH?

The planet is at least as big as Jupiter and almost surely

gaseous. It would not harbor life as we know it. And because it

orbits a dying star, any other planets in the system would not

receive the sort of life-giving heat and light provided by the sun.

But since the object's initial eons were spent around a

sunlike star, astronomers said it's possible it had a neighbor

somewhat like Earth, a place where life might have found opportunity

at a time when our sun wasn't even a glimmer in eyes of the cosmos.

In this Hubble image, the white arrow points to a burned-out white

dwarf star. Radio astronomers discovered the white dwarf and another

burned-out star - a rapidly spinning neutron star, called a pulsar -

a decade ago. Observations also picked up the gravitational signature

of a third unseen celestial body, which scientists now say appears to

be a planet.

Steinn Sigurdsson, a Penn State University researcher who

led the work, said the Jupiterlike planet formed in a nearly circular

orbit, somewhere between two and eight times as far from a star as

Earth is from the sun. That orbit would have been favorable to the

development of an Earthlike planet, a so-called "terrestrial."

"This [orbit] is wide enough that a terrestrial planet could

have comfortably fit in the habitable zone — if [the terrestrial]

formed in the first place," Sigurdsson told Space.com. "It certainly

makes it more likely that planets capable of hosting life could have

formed earlier than hitherto thought. Possibly much earlier and much

more commonly."

Any Earthlike planet that might have developed inside the

orbit of the gas giant — and there is no evidence that one did —

would have been destroyed during a later bout with gravitational

chaos.

 

THE PLANET'S CHAOTIC HISTORY

 

The planet was forged from gas around a newborn yellowish

star in an ancient "globular" star cluster called M4, 7,200 light-

years away and within our Milky Way Galaxy. Its existence was first

suspected in 1992.

Recent Hubble Space Telescope observations allowed Sigurdsson

and his colleagues to devise a remarkable tale of the planet's

presumed journey.

About 2 billion or 3 billion years ago, as the yellow star and

its planet were plunging into the crowded core of M4, they passed

near a collapsed, dense and dying neutron star, an object that

resulted from some previous explosion of a very massive star.

The neutron star had an orbiting companion star. The

gravitational tug of war that ensued booted the neutron star's

companion into space. But the neutron star, a weighty competitor,

captured the yellow sunlike star and its planet.

The sunlike star aged, bloating into a red giant (our sun will

do the same one day). The red giant's gas flowed onto the neutron

star, energizing it. The neutron star spun faster. Today, it rotates

on its axis 100 times every second and is known as a pulsar.

Meanwhile, the red giant's fuel was exhausted and it turned

into a cool, fairly dim white dwarf.

The newfound planet now orbits both the white dwarf and the

neutron star.

"We probably would never have found this planet if it had just

stayed with its original star," Sigurdsson said. "Its history put it

in the right place; the interactions helped us see it."

 

END TO CONTROVERSY

 

February 10 — NASA video explains the scientific search for signs of

life beyond Earth and the solar system.

 

Researchers discovered the pulsar, named PSR B1620-26, and

its companion white dwarf star in the late 1980s. The planet was

first suspected in 1992, but some astronomers thought the data showed

a third, distant orbiting star, rather than a close-in planet.

"By 1999 we knew the object was low-mass, with a significant

probability it was a planet," Sigurdsson said.

Ending a decade of controversy, the new Hubble observations of

the neutron star's white dwarf companion, and how the objects wobble

in space due to the gravitational tugs, allowed Sigurdsson's team to

measure the trajectory and mass of the suspected planet. They

confirmed that it is indeed not large enough to be anything else. The

data, along with knowledge of the stars' ages, also allowed them to

trace the planet's remarkable history.

The planet has not been seen or imaged directly, so final

proof of its existence awaits further study.

It is estimated to be 2.5 times the mass of Jupiter. Its heft

might equal Jupiter's, Sigurdsson said, and it is definitely no

lighter. There's a slight chance it is a few times Jupiter's mass.

The planet's orbit is about 100 years long. It goes around the

two old stars at a distance that is most likely similar to Uranus'

distance from the sun.

At 7,200 light-years from Earth, it is not just the oldest

known planet but also the farthest.

The results are detailed in Friday's issue of the journal

Science.

 

MIND-BOGGLING

 

There are many strategies in the search for extraterrestrial life.

Which do you think could be the most fruitful?

 

Looking for traces of ancient life on Mars.

Exploring the moons of Jupiter and Saturn.

Listening for faraway radio signals.

Investigating distant Earthlike planets.

None of the above.

 

 

Vote to see results

 

There are many strategies in the search for extraterrestrial life.

Which do you think could be the most fruitful?

* 19212 responses

Looking for traces of ancient life on Mars.

19%

Exploring the moons of Jupiter and Saturn.

11%

Listening for faraway radio signals.

17%

Investigating distant Earthlike planets.

42%

None of the above.

12%

 

Survey results tallied every 60 seconds. Live Votes reflect

respondents' views and are not scientifically valid surveys.

 

The planet exists in an unlikely place. Astronomers assumed

the gravitational interactions in a globular cluster — M4 contains

100,000 tightly packed stars — would rip planetary systems apart.

"This is tremendously encouraging that planets are probably

abundant in globular star clusters," said study team member Harvey

Richer of the University of British Columbia.

But it's the object's apparent history that has astronomers

reeling.

"The fact that this system managed to form a gas-giant planet

12.7 billion years ago certainly boggles the minds of those of us who

are used to having a hard time going back just 4.5 billion years in

time," said Alan Boss, a leading planet-formation theorist at the

Carnegie Institution of Washington.

Boss, who was not involved in the discovery, said the tortured

history of the system implies there is no life there now. And back

when it formed, there would have been less rock — the stuff of a

terrestrial planet — because heavier elements form with subsequent

generations of stars.

But there would have been some rock, and Boss agrees that the

discovery suggests life might have had a chance.

"If there were gas giants around at 12.7 billion years ago, I

would think that there could be a few terrestrial-like planets too,"

Boss said in an e-mail interview. "Presumably some of them [would

have] experienced a more gentle history than this poor world, and so

some might have experienced some sort of flirtation with life, if not

something much more serious."

 

FRESH VIEW OF PLANET FORMATION

More certain, Boss said, is that the primeval planet supports

his own radical model of planet formation.

Building on the controversial work of others, Boss last year

proposed that all the giant planets in our solar system formed via

direct collapse of material in a disk of leftover stuff that circled

the newborn star.

The model, "wild" even by Boss' reckoning, is called "disk

instability."

The standard model of planet formation — which all experts

agree no longer explains all of reality — held that gas giant planets

formed after a rocky core larger than Earth had first assembled. The

massive rocky core then attracted lots of gas.

But this so-called "core accretion" model takes considerable

time, and there has to be a lot of rocky material available.

 

• More on the Life and Times of the Primeval Planet

• Timeline of the Discovery

• Graphic: The Oldest Known Planet's Bizarre Odyssey

• Graphic: Two Ways to Build a Planetary System

• Earth-Sized Planets Confirmed, But They're Dead Worlds

• Celestial Soulmates: Jupiterlike Planet Found in System Similar to

Ours

• Alien Worlds Through the Eyes of Artists

 

 

The newfound planet may have formed too quickly for core

accretion to be responsible.

Boss points out that the early universe was composed mostly of

gas. Stars in the M4 cluster have just one-twentieth the amount of

rocky or metal material that exists in the sun, he said. That implies

a slow rate of growth for a rocky core and probably the lack of

sufficient mass to build a Jupiterlike planet through core accretion.

"Disk instability would seem to be the only hope in a system

composed almost entirely of hydrogen and helium," he said.

The newfound planet is not the first found orbiting a pulsar.

Another trio of planets — all about the size of Earth — orbit

the pulsar PSR 1257+12. They were confirmed to exist just two months

ago and, prior to that, their presence had long been suspect.

The Earth-sized pulsar planets, found by Alex Wolszczan (also

of Penn State), are a different breed, however. They probably formed

after the stellar explosion that created the dying star they go

around, Boss said. So they are almost surely devoid of life and never

could have supported any.

The International Astronomical Union lists Wolszczan's worlds

in its catalogue of extrasolar planets. But other planet hunters

choose not to list them, partly because their formation and

environment is so different, and partly because they are not

considered habitable and so are not as important in the search for

life.

The newfound pulsar planet, having presumably formed around a

normal star, is unlikely to be ignored. Its discovery brings the

total of known extrasolar planets, counting Wolszczan's, to 121.

 

© 2003 Space.com. All rights reserved.

 

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Interesting, isn't it? What to the devotees think of this? And, any

idea what planet they may have discovered in our universe?

 

YS,

Prtha dd