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Approach of Asteroid 3200 Phaethon to Earth in December 2017

Russian version

    In mid-December 2017, the asteroid 3200 Phaethon will make a close approach to the Earth. It is a small asteroid with a diameter of about 5 km. Although its size is quite small in comparison with biggest asteroids of the Solar System, it is one of the largest objects among those crossing the Earth's orbit. Despite the fact that, according to its orbital parameters, Phaethon refers to potentially dangerous astronomical objects, it will not present any danger to the Earth in the next few centuries.
    The asteroid will continue approaching the Earth up to mid-December 2017. During this time, owing to distance decrease, its magnitude will increase reaching its maximum on December 14-15. The minimum distance between the Earth and Phaethon will be in the night on December 16-17.
    Phaethon will not be observable with the naked eye. Its maximum brightness will be about 11 magnitudes. This means that its brightness will be about a hundred times smaller than the brightness of faintest stars observable with the naked eye. Amateur astronomers will be able to observe it with 15-cm-diameter telescopes or larger. It will be seen as a weak point for them, moving against the stellar background. Even for biggest ground-based telescopes, it will be indistinguishable from a point without special observation methods. Although, with high angular resolution techniques such as speckle-interferometry or adaptive optics, its angular sizes will be sufficient for resolution at large telescopes.
    Observers in European Russia will be able to observe Phaethon in the evening and night on December 14, 15, and 16. For Moscow, the climax point will be passed on December 14 at 9:40 p.m., December 15 - at 8:30 p.m., on December 16 - at 7:25 p.m. local time. The altitude at this point in Moscow will be 77, 72, and 64 degrees respectively.
    The shortest distance to Phaethon is about 10.3 million kilometers, or 0.069 astronomical units (one astronomical unit is the average distance between the Earth and the Sun). As a comparison, the average distance to the Moon is shorter than 0.4 million kilometers. However, such approaches are quite rare. The next two comparable in distances will occur in 2050 and 2060. Phaethon will be closer to the Earth only in 2093, when the distance to it will be about 3 million kilometers.
    Phaethon has an elongated orbit more characteristic of comets rather than of asteroids. The point in its orbit nearest to the Sun (perihelion) is at a smaller distance than the orbit of Mercury (the nearest planet to the Sun), and the most distant point is farther than Mars (the fourth planet from the Sun). At the moment, it shows a dusty tail which also makes it similar to comets. Even before it was discovered, it was concluded from the trajectory of its movement that Phaethon was related to the Geminids, a meteor shower. This is one of the most powerful showers in the year, and in some years it is the most powerful of the observed. It can be observed in the first half of December with a peak activity on December 13-15. At this time, the observer can see more than 100 meteors per hour with the naked eye.
    At present, the Japan Aerospace Exploration Agency plans to send the DESTINY+ probe to Phaethon. The launch is tentatively scheduled for 2022. The purpose of this mission will be to study the structure of Phaethon, as well as the physics of its dust. Thus, according to results, relative contribution of cometary and asteroid dust to interplanetary dust particles should be determined, direct measurements of physical parameters of dust tail particles should be made, and the structure of the asteroid's surface should be studied in detail.
    The approach of the asteroid Phaethon with the Earth in December 2017 is the last opportunity to study its physics with ground-based telescopes before the space mission planned.
    There is a legend about Phaethon in Greek mythology.

Contact - Dyachenko V.V., SAO RAS Junior Researcher
Fig.2. Fig.3. Fig.4.
Fig.2,3,4 - Trajectory of the asteroid Phaethon in the nights of December 14, 15, and 16, 2017. By Moscow standard time. The calculated position may vary up to several arcminutes depending on the observer's location.
Image B.E.Schmidt and S.C.Radcliffe Scientists Fig.1. Variations of distance (top left), angular sizes (top right), brightness (bottom left), and the Sun-Observer-Phaethon angle (bottom right) in December 2017 Fig.5. Expected approach of Phaethon with the Earth. The Earth's position corresponds to 0 along the vertical axis, the blue line shows the distance to the Moon