Download closing in on extrasolar earths

Closing in on Extrasolar Earths
Edna DeVore, Director of Education and Outreach, SETI Institute, SPACE.com
June 19, 2008
Little more than a decade ago, astronomers Michel Mayor and Didier Queloz announced
the discovery of a planet in orbit about 51 Pegasi. It rushes around its sun in just over 4
days, seared to a temperature of 1,000 degrees Celsius (about 1,800 degrees
Fahrenheit). Today, we call this sort of planet a "hot Jupiter." This was the first planet
found orbiting a main sequence star — a star similar to our Sun. Earlier, the irregular
beat of a pulsar revealed the cindered remains of planets orbiting the corpse of a dead
star. Most likely, they formed after the supernova death of their parent star, which
indicates that planet formation is a likely outcome from a disk of material. These pulsar
planets are not good places to live. But discovering 51 Pegasi around a more ordinary
star kicked off a great planetary gold rush.
Almost weekly, there's an announcement of yet another extrasolar planet around a
neighborhood star. This week, it's a triple system of super-Earths discovered at the
European Southern Observatory at La Silla using the HARPS (High Accuracy Radial
velocity Planet Searcher) instrument. The planets, having 4.2, 6.7, and 9.4 times the
mass of the Earth, orbit the star with periods of 4.3, 9.6, and 20.4 days, respectively.
These short periods place the trio of new planets well within the orbit of Mercury around
the Sun. So, again, these are hot planets, well inside the habitable zone of their star.
This trio, and others, were announced this week at the international conference, "Extrasolar Super-Earths," and demonstrate that small planets are likely common.
"Clearly these planets are only the tip of the iceberg," says Michel Mayor, team leader
for this discovery. "The analysis of all the stars studied with HARPS shows that about
one third of all solar-like stars have either super-Earth or Neptune-like planets with
orbital periods shorter than 50 days." These planets are like the proverbial gold nuggets
sought by the 49ers here in California. They mark the trail to the mother lode, where the
ultimate goal is to find another Earth.
Only a handful of the 300 plus planets known to exist are categorized as super-Earths.
The ground-based radial velocity method preferentially reveals Jupiter-sized planets.
They induce greater spectral shifts in their stars. Tiny terrestrial planets the size of Earth
hardly disturb their parent stars, and their radial velocity signatures are lost in the noise.
Super-Earths are beginning to be found with high-precision instruments like HARPS.
Hints of small planets have also been reported by the COROT (COnvection ROtation
and planetary Transits) Mission and by the gravitational lensing experiments underway.
But the holy grail — an Earth-size planet in the habitable zone of its star — awaits
NASA's Kepler Mission. The Kepler spacecraft launches in February 2009, 400 years
after Johannes Kepler published his first two laws of planetary motion in Astronomia
Nova, the "New Astronomy" which first described planets orbiting on ellipses and at
varying speed around the Sun. Ten years later, he published his third law which relates
the period of the planet to its mean distance from the Sun. Kepler used his discoveries to
predict solar transits of Mercury and Venus, but did not survive to observe them. Soon,
NASA scientists will seek transits to discover Earth-size planets about distant stars. And,
they named the mission in honor of Johannes Kepler.
The Kepler Mission is especially designed to discover small planets around Sun-like
stars by observing transits. The Kepler Mission will observe more than 100,000 stars for
at least 3.5 years, seeking evidence of other Earths. Lots of hot, close-in planets will be
discovered in the first months of the mission. Finding Earth-size planets in Earth-like
orbits requires patience because observations must be repeated to confirm discoveries.
If an alien astronomer in a distant solar system were looking for us, Earthly transits
would be seen once per year, and that good astronomer would require at least 3 transit
observations to announce a discovery. The same is true for the Kepler scientists.
Kepler's scientific prospectors should be announcing discoveries of Earth-size planets in
habitable zones by 2011-2012.
In my opinion, that's a short wait to answer the question, "Are there other planets like
Earth orbiting distant suns?" We're approaching the mother lode of distant solar
systems, and the Kepler Mission promises a major advance toward understanding
whether we are alone in this vast universe.
Pluto's Identity Crisis Hits Classrooms and Bookstores
Jeanna Bryner. SPACE.com
June 19, 2008
NEW YORK — Pluto was once a planet. Then, a dwarf planet. And as of last week, a
plutoid. The fall from grace has teachers, parents and educational publishers struggling
to keep up, while kids remain loyal to their favorite, the ninth planet. Underscore planet.
Last week, the International Astronomical Union (IAU) announced Pluto should now be
called a "plutoid," two years after the organization voted to demote Pluto to "dwarf
planet" status.
Meanwhile, many kids are nearly certain Pluto is still a planet.
"I think it's a planet. But me and my friends, we talk about it sometimes and we go back
and forth," said Natalie Browning, 9, sitting in a park in Manhattan with her family. "Right
now, I'm not 100 percent. I'm just 75 percent" sure that Pluto is a planet.
Natalie's mom, Bobbie Browning, said, "You've got kids with textbooks saying that Pluto
is part of the solar system and a planet, and teachers have to say it isn't [a planet]."
Science teachers and publishers already worked to update their resources to read
"dwarf planet." And now, boom, that category is out of favor among astronomers.
"Students who have just learned about the concept of dwarf planets must now be taught
the new concept of plutoid," said Janis Milman, who teaches earth science at Thomas
Stone High School in Maryland. "This will lead to confusion in the classroom and
resistance to learning the new terms, because the students will question, why learn
something that might change again in a year or so?"
A cursory survey at a large chain bookstore here revealed three out of four books
published in 2006 or later were updated, with Pluto designated as a dwarf planet and the
solar system said to include just eight planets.
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Chronicles of Pluto
Discovered in 1930 by Clyde W. Tombaugh at Lowell Observatory in Arizona, Pluto was
always considered an oddball of sorts, with its tiny size (smaller than some moons) and
eccentric orbit. During its 248-year trek around the sun, Pluto swings from its farthest
point from the sun at 49.5 astronomical units (AU) to as close as 29 AU from the sun.
One AU is the average distance between the Earth and sun, or about 93 million miles
(150 million kilometers).
More than 70 years later, in August 2006, 424 astronomers at an IAU meeting voted to
demote Pluto to dwarf planet status. Last week, the IAU Executive Committee
reclassified Pluto as a plutoid. The other object in the plutoid club, Eris, is larger and
more massive than Pluto.
Astronomers expect to find hundreds of Pluto-sized objects. And so the fate of Pluto will
determine how these worlds are classified. For instance, new computer modeling
suggests an object up to 70 percent of Earth's mass is lurking beyond Pluto. This "Planet
X," if confirmed, would be called a plutoid under the IAU's scheme.
No matter what the scientists say, many kids won't let go.
"It's a planet," said fifth-grader Emily Mitchell, whose mother Laurie agreed, saying, "I
grew up learning it was a planet."
"It's the smallest planet," said Liam, a 4-year-old who is "about to be 5." Liam's teacher
Rachel Kaplan said, "I was really sad when Pluto was declassified as a planet, because
I've studied astrology for a number of years."
Aileen Wilson said her 7-year-old son is interested in Pluto's label. "He's interested in
why it was a planet and why it's not a planet anymore."
"I know that it was demoted and it's not a planet. But I don't know what it's called," said
Erin Kelly, a pre-school teacher sitting on a park bench with her students in New York.
In the classroom
Even as scientists are arguing over the "plutoid" designation, with some saying they
won't use the term, educators are already latching onto it.
Change is the name of the game in science, according to Gerry Wheeler, the executive
director of the National Science Teachers Association.
"Basically, it's a teachable moment for science teachers, because it shows the dynamic
nature of science," Wheeler told SPACE.com. He added the NSTA will spread news of
the plutoid category to science teachers in the fall.
Elementary school science teacher Lucy Jensen agrees: "Pluto has made it interesting
studying our planets this year." She teaches at Joliet Public School in Montana. "Our
only problem we now have is buying new material, such as posters, videos, DVDs and
game/study materials that need to be updated," she said.
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Jensen added that while her fourth-grade students were more upset than the third
graders about Pluto's demotion, the parents were the most upset. "It is hard to teach old
dogs new tricks, and we like what we know," she said.
"Time has always been taken in the classroom to ponder the origin of Pluto. When Pluto
became a dwarf planet, along with Eris and Ceres, it made it easier to explain why an
object of Pluto's small stature could be classified," high-school teacher Milman said.
"Now we will just need to teach them more new definitions."
Milman added that "dwarf planets" is an easier term for students to grasp compared with
plutoids. "Objects of Pluto, Eris and Ceres' size are too small to be called planets so they
were called dwarf planets. That was easier for the students to understand," she said.
Yet many students are still unaware of the change made in 2006.
"My fourth graders still consider Pluto a planet," said Bev Grueber, a science teacher at
North Bend Elementary in Nebraska. "We do extensive oral reports on the planets to
meet a state standard, and everyone jumps for joy when they get Pluto. Last year, I left
Pluto out of the draw and they asked where it was, so they still consider it a planet
regardless of what the space scientists tell us the definition of that planet is."
Aram Friedman, who founded Ansible Technologies Ltd. in New Jersey, travels to
schools to teach about astronomy using a portable planetarium. In a typical fifth-grade
class, he teaches students the features of the inner planets and the outer planets. Pluto,
he says, doesn't fit into those categories. That makes sense to kids.
Publishing lag
Many science textbooks have only recently caught up with the dwarf planet concept.
For publisher McGraw Hill Education, the 2008 elementary and secondary school
science textbooks describe Pluto as a dwarf planet.
Middle schools with the current Holt Science and Technology textbooks would see Pluto
defined as a dwarf planet. McDougal Littell Science took a slightly different approach.
"We didn't say how many planets there were, so we didn't have to make a lot of
changes. We explained, historically, that it had been classified as a planet when it was
discovered," said Dan Rogers, vice president and director of Holt McDougal's science
and health product development.
McDougal's teacher's edition included a detailed explanation of Pluto's dwarf planet
status.
"One of the reasons we were cautious is because we thought the whole thing was
unresolved and was going to change again," Rogers said. "We're in the process of
developing a brand new program, a new set of books."
In "Traveler's Guide to the Solar System," an astronomy book published in 2007 for kids
age 8 to 10, the author notes, "Earth is the third of nine planets (some say eight, some
say ten, but nine is kind of traditional), orbiting our local star, the Sun."
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Starry Night, astronomy software that includes educational resources, refers to Pluto as
a dwarf planet, according to content director Pedro Braganca. (Starry Night is a division
of Imaginova Corp., which also owns SPACE.com.)
And soon, educational publishers may need to re-update material. Word has it
astronomers are vowing to pursue a reinstatement of Pluto as a planet.
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