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First results on the Pluto system by New Horizons
The first scientific results regarding the Pluto system as observed from New Horizons have been published in Science [1]. It is impressive to see direct images and maps of such distant worlds.
Maps of Pluto (A) and Charon (B) with
informal feature
names (see Fig. 2 and text in Stern et al. 2015, for more details).
More remarkable is the complex geology and geomorphology which characterize both Pluto and Charon. Pluto is by far a non-dead planet as resurfacing is indicative is some areas, which is puzzling as there are no obvious energy sources for such activity. Moreover, water ice may be the basis for the formation of high mountains (up to 2-3 km) as N2, CO, and CH4 cannot form such structures.
Pluto’s atmosphere, as measured by solar UV absorption, is characterized by N2 at ~1670km, CH4 below ~960km, C2H4 at ~300km, haze below ~150km, and C2H2 at ~50km. Additionally, UV and high-energy radiation interact with the these particles giving raise to tholins (a form of organic molecules).
The other two moons to be observed, Nix and Hydra, displayed high albedo, probably due to cleaner (compared to what is found in Charon) water ice – another puzzling issue since there is a number of processes that could darken their surfaces (like transfer of darker material from Charon or Kuiper meteorites).
More results are forthcoming, since there are data (e.g. UV spectra) that have not been downlinked from the satellite yet.
[1] Stern et al., 2015, Science, vol. 350, 292,
or arXiv:1510.07704
Pro-Am collaborations in Planetary Astronomy – review paper
This is a great collective work on various professional-amateur collaborations (written by both professionals and amateurs) regarding aspects of Planetary Astronomy, such as: terrestial planets (Mercury, Venus, Mars), gaseous planets (Jupiter, Saturn, Uranus, Poseidon), interstellar dust (meteoroids, meteors, fireballs, meteorites), Jupiter impacts, Lunar flashes, asteroids, comets, Kuiper belt objects and Centaurs, exoplanets.
I find it a really inspiring paper for both kinds! I hope that we will see more of these collaborations in the future, since the is a continuous advance in amateur contributions to Astronomy during the last decades.
New planet around a binary system
It is always fascinating when science fiction becomes reality. This is the case with the Kepler-16b, a binary system that proved to host a cold giant planet (like Saturn), which compiles from gas and rocks. This opens a wide new category of planetary systems since most of the stars belong to a binary system.
For more information see NASA’s Kepler announcement and the related page with star/planet’s properties, along with the publication (Doyle L et al 2011: Science – in press, arXiv-1109.3432).
Kepler’s first results
Kepler is a space based telescope to study a small area between Cygnus and Lyra for exoplanet transits of all possible targets but mainly to find Earth sized candidates in the habitable zone. A fist publication reveals these numbers:
“On 1 February 2011 the Kepler Mission released data for 156,453 stars observed from the beginning of the science observations on 2 May through 16 September 2009. There are 1235 planetary candidates with transit like signatures detected in this period. These are associated with 997 host stars. Distributions of the characteristics of the planetary candidates are separated into five class-sizes; 68 candidates of approximately Earth-size (radius < 1.25 Earth radii), 288 super-Earth size (1.25 Earth radii < radius < 2 Earth radii), 662 Neptune-size (2 Earth radii < radius < 6 Earth radii), 165 Jupiter-size (6 Earth radii < radius < 15 Earth radii), and 19 up to twice the size of Jupiter (15 Earth radii < radius < 22 Earth radii). In the temperature range appropriate for the habitable zone, 54 candidates are found with sizes ranging from Earth-size to larger than that of Jupiter. Five are less than twice the size of the Earth. Over 74% of the planetary candidates are smaller than Neptune. The observed number versus size distribution of planetary candidates increases to a peak at two to three times Earth-size and then declines inversely proportional to area of the candidate. Our current best estimates of the intrinsic frequencies of planetary candidates, after correcting for geometric and sensitivity biases, are 6% for Earth-size candidates, 7% for super-Earth size candidates, 17% for Neptune-size candidates, and 4% for Jupiter-size candidates. Multi-candidate, transiting systems are frequent; 17% of the host stars have multi-candidate systems, and 33.9% of all the candidates are part of multi-candidate systems.” [ Borucki WJ et al 2011, arXiv1102.0541v1 ]
And all these in 105 square degrees field of view which is (well, rather large for an astronomical instrument) only a small part of the whole sky, only 1/400 ! The numbers are more exciting if we include the fact that all of these systems are transits which means that a specific geometry is needed in order to see the dimming of the stars’ brightness due to the pass of the planet(s) in front of them. But more time is needed to validate these results as the transits must been seen again and again in order to be sure that what is seen is real and not something else, that’s why they are candidates and not confirmed planets yet. But still the numbers are huge and … promising!
More exciting results include the fact that before Kepler none Earth-sized candidates or candidates inside the habitable zone were known and now there are 68 and 54 candidates respectively. In addition, complex systems are discovered like the Kepler-11 which has 6 planets [ Lissauer JL et al 2011, Nature & arXiv1102.0291 ] and a rocky planet [Batalha NM et 2011 – arXiv1102.0605 ].
As stated by the NASA Administrator Charles Bolden: ” In one generation we have gone from extraterrestrial planets being a mainstay of science fiction, to the present, where Kepler has helped turn science fiction into today’s reality “.
Geminids and their mysterious parent body 3200 Phaethon
The Geminids are one of the best meteor showers of the year with numerous (ZHR~120) and bright (r~2) meteors! The parent body is an asteroid named 3200 Phaethon, which is believed to be a candidate for an extinct cometary nucleus, a mystery by itself. Moreover, during the last perihelion passage of the asteroid its magnitude increased unexpectedly (almost doubled), which is thought to be connected to some ejected dust originated from break-down of surface rocks. But this dust can account only for the 0.01% of the total material which is needed to supply the stream in order to see this activity each year this show.
How this object has manage to give out so much material? Geminids are not ready yet to reveal their mysteries…
The source and paper ( by journal or author) / Jewitt D. & Li J., Activity in Geminid parent (3200) Phaethon, AJ, 140, 1519, 2010.
Hypervelocity star – HE 0437-5439
An interesting story on hypervelocity stars. Around 16 know since 2005, one of them being the HE 0437-5439 which travells at 2.5 million kilometers / hour. The puzzle about this is that it is too young to have travelled so far from the Wilky Way (200 000 light-years over the disk plane).
The story (?):
“A hundred million years ago, a triple-star system was traveling through the bustling center of our Milky Way galaxy when it made a life-changing misstep. The trio wandered too close to the galaxy’s giant black hole, which captured one of the stars and hurled the other two out of the Milky Way. Adding to the stellar game of musical chairs, the two outbound stars merged to form a super-hot, blue star.”
Hubble NewsCenter release & the ApJ Lett paper / Warren R. B. et al, A galactic origin for HE 0437–5439, the hypervelocity star near the Large Magellanic Cloud, ApJ, 719, L23, 2010.
How big a star can be?
It seems that this question has no final answer yet. Although the recent models were claiming that no star bigger than 100-150 solar masses can exist, there is evidence that a star close to 300 solar masses exists in the Large Magellanic Cloud. One star, R136a1 (from the young cluster RMC 136a or R136), is considered to have a mass ~265 solar masses (with a birthweight close to 320 solar masses).
More on ESO’s announcement (eso1030) & the paper (2010arXiv1007.3284C / Crowther P.A. et al, The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150Msolar stellar mass limit, MNRAS, 408, p 731, 2010)
