[meteorite-list] Target Asteroid 65803 Didymos

[Ron Baalke]

http://www.esa.int/Our_Activities/Space_Engineering_Technology/Asteroid_Impact_Mission/Target_asteroid

Target Asteroid
European Space Agency
February 2, 2016

The target of the AIM mission is asteroid 65803 Didymos (1996 GT), an 
Apollo-type near-Earth object (NEO) with a perihelion (minimum distance 
to the Sun) that is just below the aphelion radius (maximum distance to 
the Sun) of Earth orbit. Didymos is a binary asteroid; the primary body 
has a diameter of around 775 m and a rotation period of 2.26 hours, whereas 
the secondary body (informally called Didymoon) has a diameter of around 
165 m and rotates around the primary at a distance of around 1.2 km in 
around 12 hours.
 
In 2015 telescopes around the globe homed in on the Didymos system to 
study the shape and size of the double asteroid and try to ascertain the 
orbital pole of Didymos and refine the shape model of the primary, among 
other things, to help plan ESA's AIM mission proposal, which is part 
of the AIDA project.

The orientation of Didymoon's orbit with respect to the ecliptic is 
one of the key factors involved in planning the AIM/AIDA mission. It is 
important, for example, in calculating the approach of the spacecraft 
to the binary system, as well as to know when the asteroid moon will fall 
into shadow - needed for scheduling payload operations. The information 
obtained during the latest observation period was put together with already 
known data to refine the orbital pole of the primary, its shape and other 
dynamical parameters, putting constraints on the bulk density of the two 
bodies.

A preliminary shape model of the Didymos primary could be extracted from 
previous radar observations in combination with new lightcurve data.

When the AIM spacecraft has arrived at the binary system it will collect 
extensive amounts of data on both the primary and secondary asteroid, 
including precise measurements of the asteroid's mass and shape and 
thermal imaging of the surface to understand the structure and mineralogical 
composition of the soil.

Thermal imaging

A variety of measuring techniques will be available through the instruments 
on board AIM and its lander/cubesats (see Payload) to comprehensively 
detail the Didymos system before DART, the impactor, will hit Didymoon. 
In particular, direct information on the internal structure of an asteroid 
will be obtained for the first time. AIM will watch the impact and will 
again collect masses of data after impact to be able to calculate the 
effect of the impact on both the shape, structure and orbit of Didymoon 
around the primary.

The thorough study of Didymoon and its impact by DART will be the first 
fully documented impact experiment at asteroid scale and will offer valuable 
insights into the origin and history of our Solar System that need a better 
understanding of the impact process at large scales. It will also provide 
scientists invaluable data to develop and assess the efficiency of  planetary 
defense strategies against any incoming asteroids in the future.

Despite Didymos' close encounter with the Earth in 2022, this asteroid 
poses no threat as there is no risk of impact. It is therefore the ideal 
candidate to run an asteroid mitigation precursor experiment whose objective 
is to change the orbit of Didymoon around its primary main body thus leaving 
the binary asteroid's path around the Sun unchanged. Such experiment will 
give us crucial information about whether the kinetic impactor technique 
would work to deflect an asteroid if ever one was discovered to be headed 
our way.