More Planets than Stars – But Axial Tilt is the Key to Life

Planets
There is an average of more than one planet per star in the Milky Way
Image Credit: NASA / ESA / ESO

With the forthcoming publication in the journal Nature on 12 January, it is estimated that there are more than 100 billion planets in our Milky Way galaxy. That means more than one planet per star, and results show that there are more rocky small Earth-like planets than giant Jupiter-size gas planets.

Most recent discoveries have come from the Kepler Observatory using transit observations. Some of the earliest confirmation of gas giants came from radial velocity Doppler observations.

The conclusions in the Nature article are based on micro-lensing studies.

Recent results from the Kepler Observatory have shown the existence of three small, rocky planets around the star KOI-961, a red dwarf. These three planets, named KOI-961.01, KOI-961.02 and KOI-961.03, are 0.78, 0.73 and 0.57 times the radius of Earth. The smallest is about the size of Mars (see below). Follow-up observations were made by the Palomar Observatory, near San Diego, and the Keck Observatory atop Mauna Kea in Hawaii.

KOI-961
Relative size of the three rocky planets around KOI-961
Image Credit: NASA / JPL-Caltech

Since it is now clear that rocky planets exist around millions, if not billions, of stars, the question arises as to whether there is life on them, and whether it may resemble life on Earth.

Whether a planet exists in the “Goldilocks” region around a star depends on many factors. Three factors include the type of star, how far away from the star the planet resides and the atmospheric pressure of the planet. A red dwarf, such as Gliese 581, means the planet has to be closer than the Earth to our Sun. A white hot star means the planet has to be farther away. And if the atmosphere is low, like Mars, or to high, like Venus, liquid water is not likely.

A fourth factor is axial tilt. If a planet has no axial tilt (the spin axis is perpendicular to the plane of its orbit around the star) then the polar regions freeze and the equatorial regions bake. There is little exchange between these regions due to atmospheric circulation. Axial tilt, such as the Earth has, allows distribution of heat between the equator and the poles.

Even if a planet has axial tilt, a recent study shows that interaction at a close distance (within the “Goldilocks” region) with red dwarf will eliminate axial tilt in less than 100 million years. Bacteria on Earth required 1,000 million years to evolve. Theoretically, a planet with no axial tilt could possess bands between the equator and the poles where liquid water would exist. But, it is quite possible the atmosphere would collapse, with gases being driven off into space at the very hot equator, and freezing solid on the ground at the poles. Such a possibility faces the planets around KOI 961.

Systems with stars like our Sun present better possibilities. The “Goldilocks” conditions exist much farther out, and axial tilt is eliminated much more slowly, as our Earth is witness. Systems such as Kepler-22b are good candidates.

The conclusion drawn from these studies is that systems similar to our Solar System present the best opportunities for life.

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AIAA 2011 Awards – Phoenix Section

AIAA The American Institute of Aeronautics and Astronautics made several awards to the Phoenix Section for 2011. Section Awards are for sections ranging from Very Small to Very Large. Phoenix is a Large Section. The press release and two awards for Phoenix are noted below:

AIAA ANNOUNCES SECTION AWARD WINNERS
Awards Honor Outstanding Section Programming in a Variety of Categories

September 21, 2011 – Reston, Va. – The American Institute of Aeronautics and Astronautics (AIAA) has announced its 2010–2011 Section Award winners. The Section Awards annually honor particularly notable achievements made by member sections in offering activities that fulfill the Institute’s mission in a wide range of fields. The Institute believes that vital, active sections are essential to the Institute’s health and mission.

Section awards are made annually in five categories based on size of membership. Each winning section receives a certificate and a cash award – $500 for first place, $200 for second, and $100 for third. The award period covered is June 1, 2010 through May 31, 2011.

Sections winning first-place awards will be honored at the AIAA awards luncheon on January 10, 2012, as part of the 50th AIAA Aerospace Sciences Meeting, held January 9–12, 2012 at the Gaylord Opryland Resort and Convention Center, Nashville, Tenn.

The Outstanding Section Award is presented to sections based upon their overall activities and contributions through the year.

Large: First Place: Phoenix, Ryan Carlblom, section chair

The Outstanding Activity Award allows the Institute to acknowledge sections that held an outstanding activity deserving of additional recognition.

Large: Phoenix, Ryan Carlblom, section chair. 2011 Celebration of Space Exploration and Yuri’s Night Celebration. The Phoenix aerospace community hosted two events on Saturday, April 9, 2011 in conjunction with the global Yuri’s Night celebrations. The first was a morning symposium open to the public, with speakers on the past, present, and future of space exploration. Entitled “A Celebration of Space Exploration,” and attended by about 150 people, the program included a look back fifty years at Gagarin’s historic flight and the space race between the U.S. and the Soviet Union, presented by Michael Mackowski, an aerospace engineer and long-time advocate of space exploration and development; a first-hand account of a Space Shuttle mission, by former shuttle astronaut Bill Gregory; a look at the past and future of the exploration of Mars, by Jim Bell, an astronomer and planetary scientist from Arizona State University; and a description of the educational programs available at the Challenger Space Center in Peoria, Arizona, by Kari Sliva, Executive Director. The second event was an evening party, held in conjunction with the annual Space Access Conference at the Grace Inn in Phoenix, that featured a space photo identification contest produced by AIAA member Maura Mackowski, a historian. The party attracted about 50 people, including members of many local space organizations as well as quite a few conference attendees.

Michael Mackowski is also a member of the Phoenix Chapter of the National Space Society. Congratulations to the Phoenix Section of the AIAA.

Hayabusa – Dust From Itokawa – III

The issue of the journal Science from 26 August 2011 vol 333 pp 1113-1131 has six articles on the Hayabusa sample return mission from the asteroid Itokawa. The first article is discussed here, the second here, and this is the third:

Neutron Activation Analysis of a Particle from Asteroid Itokawa

A single grain from the Hayabusa mission has been analyzed by instrumental neutron activation analysis (INAA). The grain was mainly olivine, with minor amounts of plagioclase, troilite and metal.

This grain was one of the largest returned by the Hayabusa mission. The scanning electron microprobe (SEM) results show this to be a large crystal of olivine. Small pieces of silicate were attached to the surface. Radioactive analysis indicates that the grain is relatively homogeneous.

Comparison of the INAA analysis of this grain from Itokawa with from an LL6 chondrite (St Severin) and an L6 chondrite (Modoc) indicated an elemental abundance discrepancy.

Iron (Fe) and Scandium (Sc) abundance can be determined reliably, and the ratio is determined by the differentiation of iron into the core of a body during its formation. In particular, the Fe/Sc ratios from the Earth, Moon, Mars and 4Vesta are lower than those of chondrites. The ratios from Itokawa are higher than those from terrestrial olivine, and are thus from an extraterrestrial origin. This increases confidence that Hayabusa did return samples from Itokawa.

Nickel (Ni) and Cobalt (Co) typically diffuse into a metal phase. The ratio of Ni/Co in bulk chondrites plot along a line with carbonaceous chondrites. Samples from the Earth’s crust are relatively depleted in Nickel compared to Cobalt, and thus are distinguished from the grain returned from Itokawa.

In addition, Iridium (Ir) abundances were estimated, and the result indicates that the sample must have condensed from a fractionated nebula gas where refractory siderophiles such as Iridium had already condensed and been removed.

Hayabusa – Dust From Itokawa – II

The issue of the journal Science from 26 August 2011 vol 333 pp 1113-1131 has six articles on the Hayabusa sample return mission from the asteroid Itokawa. The first article is discussed here, and this is the second:

Oxygen Isotopic Compositions of Asteroidal Materials Returned from Itokawa

The first article in this series established that the major mineral assemblages of the asteroid Itokawa are olivine, pyroxene, plagioclase, iron sulfide and iron-nickel metal.

Minerals within bodies of the Solar System have unique oxygen isotope ratios, thought to be determined by gas-dust chemistry and accretion physics. However, the Earth and the Moon are the only bodies for which isotope ratios are known.

Twenty-eight (28) of the sample grains returned by Hayabusa were analyzed for oxygen isotope abundances. The ratios were compared to the ordinary chondrite meteorite Ensisheim (an LL-6 chondrite) and Earth minerals, and the uncertainty in measurements were calibrated against standard mean ocean water (SMOW) from Earth. The results show that the grains returned by Hayabusa are not of terrestrial origin. One of the Earth minerals was a fosterite crystal from San Carlos, Arizona.

Chondrites are classed as H, L or LL, and the samples from Itokawa are clearly L or LL and not H. The variation in ratios between samples indicates the degree of equilibration due to metamorphic heating. These data indicate that the samples from Itokawa experienced temperatures between 600 C and 720 C, which is lower than LL6 chondrites and higher than LL4 chondrites.

These results are consistent with those from those reported in the first paper and provide unequivocal evidence that ordinary chondrites come from S-Type asteroids.

Is An Earth Trojan Asteroid the Logical Target for the “Flexible Path”?

Trojan Asteroid 2010 TK7
Asteroid 2010 TK7 is circled in green.
Image Credit: NASA / JPL-Caltech / UCLA

Scientists using the Wide-field Infrared Survey Explorer (WISE) have discovered the first Trojan Asteroid in Earth orbit. Trojans orbit at a location in front of or behind a planet known as a Lagrange Point.

A video of the asteroid and its orbit at the Lagrange point can be found here.

Martin Connors of Athabasca University in Canada is the lead author of a new paper on the discovery in the July 28 issue of the journal Nature.

Connors notes that:

These asteroids dwell mostly in the daylight, making them very hard to see. But we finally found one, because the object has an unusual orbit that takes it farther away from the sun than what is typical for Trojans. WISE was a game-changer, giving us a point of view difficult to have at Earth’s surface.

TK7 is roughly 300 meters in diameter and traces a complex motion around SEL-4 (Sun Earth Lagrange point 4). The asteroid’s orbit is stable for at least the next 100 years and is currently about 80 million kilometers from the Earth. In that time, it is expected to come no closer that 24 million kilometers.

The obvious question is whether this is the logical destination for NASA’s Flexible Path manned asteroid mission? The Lagrange 4 point (SEL-4) is a logical way station on the Solar System exploration highway. Other NEO asteroids that have been identified as possible targets are few and much more difficult to reach and return than an asteroid at SEL-4. This may well be the target of opportunity that opens manned exploration of the Solar System in an “easy” mode. Unfortunately, Asteroid 2010 TK7 travels too far above and below the plane of Earth’s orbit, which would require large amounts of fuel to reach it.

NEOWISE is the program for searching the WISE database for Near Earth Objects (NEO), as well as other asteroids in the Solar System.The NEOWISE project observed more than 155,000 asteroids in the main belt between Mars and Jupiter, and more than 500 NEOs, discovering 132 that were previously unknown.

A World Like Ours?

Exo Solar System
Planetary System HD 10180 Discovered By HARPS
Image Credit: European Southern Observatory

In a paper (pdf) published in the journal Astronomy & Astrophysics on 13 August 2010, scientists announced the discovery of a planetary system circling the star HD 10180, which is 127 light years from Earth.

The extraordinary aspect of the announcement is the existence of as many as seven planets in the system. Previous exo-planetary discoveries have generally been single planets in the range of Jupiter and above. Currently, and this list will be obsolete when you read it, there are 488 exoplanets. There are 15 known systems with at least three planets, and the previous record holder has five planets, with two of them being in the Jupiter class.

Christophe Lovis, lead author of the paper, stated

“This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets. Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system.”

The science team is certain of the existence of five planets, whose masses are in the range of Neptune. These five planets have orbits that range from 6 to 600 days. The planets are all located in orbits around HD 10180 that are between 0.06 and 1.4 times the distance of the Earth from our Sun. This puts all five within the orbit of Mars, and the orbits of these planets are almost circular.

A sixth planet is suspected, which has an orbit lasting 2,200 days, and is considerably farther away. Its mass is about that of Saturn. The seventh planet has a mass 1.4 times that of Earth, and orbits the star in 1.18 Earth days.

The research team is composed of C. Lovis, D. Ségransan, M. Mayor, S. Udry, F. Pepe, and D. Queloz (Observatoire de Genève, Université de Genève, Switzerland), W. Benz (Universität Bern, Switzerland), F. Bouchy (Institut d’Astrophysique de Paris, France), C. Mordasini (Max-Planck-Institut für Astronomie, Heidelberg, Germany), N. C. Santos (Universidade do Porto, Portugal), J. Laskar (Observatoire de Paris, France), A. Correia (Universidade de Aveiro, Portugal), and J.-L. Bertaux (Université Versailles Saint-Quentin, France) and G. Lo Curto (ESO).

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Kepler

NASA has announced that the Kepler Mission has released the first 43 days of science data on more than 156,000 stars.

Kepler is designed to continuously monitor a star field in the constellations Cygnus and Lyra. The objective is to find Earth like planets circling solar-like stars in what is known as the Habitable Zone, the region around a star where water can exist as a liquid. Since planetary orbits in this region take about a year to complete, the Kepler mission is designed to last through November 2012. This will allow Kepler to catch a planet fitting the description making three transits of its star during the three and a half year mission. Kepler was launched 6 March 2009.

When a planet transits a star, it blocks some of the light from the star. If an observatory is looking at the star at just the right moment, it will see the star dim and then brighten again when the planet finishes passing in front of the star. The effect is very small. A transit will dim the starlight by 100 parts per million, and last from 2 to 16 hours if the planet is in the habitable zone.

Kepler is designed to monitor 100,000 stars continuously for three and a half years. This is enough time to capture three transits by a planet. Kepler has only one instrument on board. This is a 0.95 meter telescope equipped with a photometer. The telescope has a large field of view in order to capture all the stars simultaneously. The field of view is about the size of your hand held at arms length (105 square degrees).

Data from the Kepler mission is archived at Space Telescope Science Institute. The three missions in which the Institute participates are Hubble, the James Webb Space Telescope, and Kepler.

Kepler Diagram
Diagram of the Kepler Spacecraft
Image Credit: NASA

Kepler Photometer
Kepler Photometer Focal Plane Assembly
Image Credit: Ball Aerospace

The photometer (left) is a single instrument, composed of 42 Charge Coupled Devices (CCDs). Each of the square units in the image are two 25 mm x 50 mm CCDs, each comprised of 2200×1024 pixels.

The CCDs are read every three (3) seconds and the data is integrated over 30 minutes. The instrument has the ability to detect an earth sized object transiting a star in 6.5 hours of integrated data.

The instrument has a spectral bandpass from 400 nm to 850 nm. Data from the individual pixels that make up each star of the 100,000 main-sequence stars are recorded continuously and simultaneously. The data are stored on the spacecraft and transmitted to the ground about once per month.

The targeted region of space and the star field in the field of view can be seen here.

At right is the Kepler spacecraft during construction. The size of the Solar Array and the Telescope (wrapped in gold foil) can be seen compared to the technician working on the Solar Array.

The scientific objective of the Kepler Mission is to explore the structure and diversity of planetary systems. This is achieved by surveying a large sample of stars to:

  • Determine the percentage of terrestrial and larger planets that are in or near the habitable zone of a wide variety of stars
  • Determine the distribution of sizes and shapes of the orbits of these planets
  • Estimate how many planets there are in multiple-star systems
  • Determine the variety of orbit sizes and planet reflectivities, sizes, masses and densities of short-period giant planets
  • Identify additional members of each discovered planetary system using other techniques
  • Determine the properties of those stars that harbor planetary systems

Kepler
Kepler with Solar Array (interior)
Image Credit: NASA and Ball Aerospace

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