Current NEO statistics
More than 200 NEOs were discovered last month, the highest rate since April 2014.
- Known NEOs: 15 934 asteroids and 106 comets
- NEOs in risk list*: 612
- New NEO discoveries since last month: 206
- NEOs discovered since 1 January 2017: 525
*The risk list of all known objects with a non-zero (although usually very low) impact probability can be found at http://bit.ly/neorisklist
The closest approach distance is not the only important parameter for assessing the asteroid hazard. The velocity plays a crucial role in shaping the outcome of a close encounter as well as in evaluating the consequences of an impact. The speed at which an asteroid flies by the Earth results from geometrical and dynamical considerations characterizing its pre-encounter orbit. A NEO with an orbital path closely resembling that of the Earth has an extremely low relative velocity at encounter, thus remaining under its gravitational attraction sometimes long enough to be captured as a temporary satellite. An object in retrograde motion (i.e. orbital inclination larger than 90°) would head face-on toward our planet, a worst-case scenario for an impact. Luckily this is a very rare occurrence: only 2 NEAs in retrograde orbits are known.
Upcoming interesting close approaches
A low-velocity encounter and the fly-by of a large asteroid happen in April.
- The 2017 FT102 close approach on 3 April was characterized by an extremely low velocity with respect to the Earth. Although the encounter was not particularly close, occurring at about the distance of the Moon, it results in a significant bending of the trajectory (see figure).
- 2014 JO25 is a km-sized object having a close approach to Earth on 19 April, at 4.6 lunar distances. During the fly-by, it will almost reach magnitude 10
Recent interesting close approaches
Seven known objects came closer than the Moon in March.
- 2017 EA with an estimated diameter of 2-3 meters was observed only few hours before its approach on 2 March (Source: NASA).
- 2017 FN1, a tiny object with a diameter of a few meters, flew by on 21 March at 63 000 km from the Earth centre. It was observed by only two observatories and for less than 12 hours before fading into twilight.
- 2017 FS, 2017 FM1, 2017 FD3, 2017 FJ101 and 2017 DS109 came closer than the Moon during the month of March. They were all small, between 5 and 30 metres in diameter, and reached between magnitude 15 and 17 at their brightest.
News from the risk list
Five new objects were added to the upper part of our risk list.
- 2017 FO63, 2017 FB1, 2017 FR102, 2017 FC3 and 2017 FN1, discovered in the second half of March, entered the risk list with a Palermo Scale higher than –6.
- IAUS 330: Astrometry and Astrophysics in the Gaia sky, 24–28 April 2017, Nice, France http://www.iau.org/science/meetings/future/symposia/1163/
- IAA Planetary Defense Conference, 15–19 May 2017, Tokyo, Japan http://pdc.iaaweb.org/
- Summer School on “Natural Space Risks”, 28 August–1 September 2017, Paris, France https://nsr-2017.sciencesconf.org/
- CELMEC VII, 3–9 September 2017, San Martino al Cimino (VT), Italy http://adams.dm.unipi.it/~simca/celmecVII/index.html
Brightest fly-bys of the decade
List of NEOs which in the past decade became brighter than magnitude 11 at close approach. Note that asteroid Duende is also known with the provisional designation 2012 DA14. Miss distances are from the centre of the Earth.
Source: Monthly newsletter from ESA’s NEO Coordination Centre | April 2017 (if not stated otherwise)