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.
Contact - Dyachenko V.V., SAO RAS Junior Researcher
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
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.
Image B.E.Schmidt and S.C.Radcliffe Scientists
Variations of distance (top left), angular sizes (top right),
brightness (bottom left), and the Sun-Observer-Phaethon angle
(bottom right) in December 2017
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