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Title: Terrestrial Planet Formation: Constraining the Formation of Mercury
Author: Patryk Sofia Lykawka, Takashi Ito

The formation of the four terrestrial planets of the solar system is one of the most fundamental problems in the planetary sciences. However, the formation of Mercury remains poorly understood. We investigated terrestrial planet formation by performing 110 high-resolution N-body simulation runs using more than 100 embryos and 6000 disk planetesimals representing a primordial protoplanetary disk. To investigate the formation of Mercury, these simulations considered an inner region of the disk at 0.2-0.5 au (the Mercury region) and disks with and without mass enhancements beyond the ice line location, aIL, in the disk, where aIL = 1.5, 2.25, and 3.0 au were tested. Although Venus and Earth analogues (considering both orbits and masses) successfully formed in the majority of the runs, Mercury analogues were obtained in only nine runs. Mars analogues were also similarly scarce. Our Mercury analogues concentrated at orbits with a ~ 0.27-0.34 au, relatively small eccentricities/inclinations, and median mass m ~ 0.2 Earth masses. In addition, we found that our Mercury analogues acquired most of their final masses from embryos/planetesimals initially located between 0.2 and ~1-1.5 au within 10 Myr, while the remaining mass came from a wider region up to ~3 au at later times. Although the ice line was negligible in the formation of planets located in the Mercury region, it enriched all terrestrial planets with water. Indeed, Mercury analogues showed a wide range of water mass fractions at the end of terrestrial planet formation.

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MESSENGER Finds Evidence of Ancient Magnetic Field on Mercury

Mercury's magnetic field, generated by a dynamo process in its outer core, has been in place far longer than previously known, a paper by MESSENGER Participating Scientist Catherine Johnson reports.
About 4 billion years ago, Mercury's magnetic field could have been much stronger than today, as indicated by low-altitude observations made by NASA's MESSENGER spacecraft that revealed evidence of magnetization of ancient crustal rocks on Mercury.
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Mercury 'painted black' by passing comets

Mercury's dark surface was produced by a steady dusting of carbon from passing comets, a new study says.
Mercury reflects very little light but its surface is low in iron, which rules out the presence of iron nanoparticles, the most likely "darkening agent".
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Title: Impact cratering on Mercury: consequences for the spin evolution
Authors: Alexandre C. M. Correia, Jacques Laskar

Impact basins identified by Mariner 10 and Messenger flyby images provide us a fossilised record of the impactor flux of asteroids on Mercury during the last stages of the early Solar System. The distribution of these basins is not uniform across the surface, and is consistent with a primordial synchronous rotation (Wieczorek et al. 2012). By analysing the size of the impacts, we show that the distribution for asteroid diameters D < 110 km is compatible with an index power law of 1.2, a value that matches the predicted primordial distribution of the main-belt. We then derive a simple collisional model coherent with the observations, and when combining it with the secular evolution of the spin of Mercury, we are able to reproduce the present 3/2 spin-orbit resonance (about 50% of chances), as well as a primordial synchronous rotation. This result is robust with respect to variations in the dissipation and collisional models, or in the initial spin state of the planet.

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The International Astronomical Union (IAU) has approved new names for twenty three craters on Mercury.

 Feature Name Diameter (km)Center LatitudeCenter Longitude
 Nabokov165.54-14.59304.27Vladimir; Russian and American writer (1899-1977).
 Mendelssohn291.0670.07257.45Jakob Ludwig Felix; German composer (1809-1847).
 Magritte148.96-72.86238.66René; Belgian painter (1898-1967).
 Kofi135.8756.79241.77Vincent Akwete; Ghanaian sculptor (1923-1974).
 Holst169.95-17.33314.9Gustav Theodore; British composer (1874-1934).
 Henri163.878.69201.08Robert; American painter (1865 1929).
 Grotell48.2571.1131.76Majlis; Finnish and American ceramist (1899-1973).
 Grainger112.61-44.11255.13George Percy Aldridge; Australian-born composer (1882-1961).
 Fonteyn29.4132.85264.31Margot; English ballet dancer (1919-1991).
 Faulkner167.848.06282.97William; American author (1897-1962).
 Ellington216.05-12.85333.82Edward Kennedy Duke; American composer, musician, conductor (1899-1974).
 Lismer139.1281.31193.28Arthur; Canadian painter (1885-1969).
 Balanchine40.938.53184.28George (Giorgi Balanchivadze); American choreographer of Georgian-Russian origin (1904-1983).
 Aksakov173.6134.7778.7Sergey; Russian author (1791-1859).
 Ailey20.5845.47182.06Alvin; American dancer and choreographer (1931-1989).
 Sousa120.746.75358.59John Philip; American bandmaster and composer (1854-1932).
 Seuss63.57.73326.76Theodor Seuss Geisel; American author and cartoonist (1904-1991).
 Petipa12.0311.52339.02Marius; French and Russian choreographer and dancer (1818-1910).
 Nureyev16.2411.63173.05Rudolf; Soviet and British ballet dancer of Tatar-Bashkir origin (1938-1993).
 Rustaveli200.552.55277.41Shota; Georgian poet (c. 1160-1216).
 Warhol91.35-2.546.08Andy, American artist (1928-1987).
 Stevenson134.071.96143.75Robert Louis; Scottish author (1850-1894).
 Pasch36.6646.14225.13Ulrica Fredrica; Swedish painter (1735-1796).

 



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Mercury has been 'dynamic world'

The planet Mercury was once an active and dynamic planet, according to new evidence from a Nasa spacecraft.
Data from the American Messenger probe shows that impact craters on the planet's surface were distorted by some geological process after they formed.
The findings, reported in Science magazine, challenge long-held views about the closest world to the Sun.
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EN0234752446M.nomap.png

The Tolstoj basin is located in Mercury's southern hemisphere, and is 355 km in diameter. This oblique image shows an elongate pit inside Tolstoj, a basin whose floor appears to have been flooded by lavas. The pit lacks the raised rim of an impact crater, and may have formed when magma withdrew from a shallow chamber, causing an unsupported area of the surface to collapse. The low-angle lighting in this image hides the floor of the pit, making it appear much deeper than it actually is. The pit is aligned approximately north-south.

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Strange Hollows Discovered on Mercury

NASA's MESSENGER spacecraft has discovered strange hollows on the surface of Mercury. Images taken from orbit reveal thousands of peculiar depressions at a variety of longitudes and latitudes, ranging in size from 60 feet to over a mile across and 60 to 120 feet deep. No one knows how they got there.
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'Hollows' mark Mercury's surface

In among a raft of papers published in this week's edition of the journal Science, researchers reveal strange hollows that pock Mercury's surface.
Irregular in shape, these depressions seem to form in the bright deposits that have been excavated where meteorites have impacted the surface.
The Messenger team cannot be sure what has caused them, but on Mars similar features are also known to exist.
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Movie of Mercury's Magnetic Equator Versus Longitude

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

This movie shows the location of Mercury's magnetic equator determined on successive orbits as the point where the direction of the internal magnetic field is parallel to the spin axis of the planet. This magnetic equator is well north of the planet's geographic equator (indicated by the horizontal grey line). The best-fitting internal dipole magnetic field is located about 0.2 Mercury radii, or 480 km, northward of the planet's center. The dynamo mechanism in Mercury's molten outer core responsible for generating the planet's magnetic field therefore has a strong north-south asymmetry.


Movie of Global Imaging Coverage to Date

Movie of MLA Coverage to Date

Movie of the Distribution of Energetic Electron Events



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