What are NEOs?
2018 LA - The Discovery of Another Very Small Impacting NEO
(4 Jun 2018) Richard Kowalski of The Catalina Sky Survey (CSS) has discovered yet another small (2-4 meter diameter) NEO just hours before it exploded harmlessly in the atmosphere above the southern regions of Africa. Detailed articles:
- JPL press release: Tiny Asteroid Discovered Saturday Disintegrates Hours Later Over Southern Africa
- MPC's discovery MPEC for 2018 LA
- AMS article: Asteroid spotted hours before impact with atmosphere over Botswana
Expect this object to be discussed further in the near future on these pages.
MPECs and Announcing Discoveries to the World
(4 Jun 2018) In the next few weeks, a series of articles will appear here to discuss NEO discovery, the NEO Confirmation Page, orbital improvement, announcement, close approaches, and communication. The goal will be to provide the reader general background information on the day-to-day operation of the IAWN. The first piece in this group will discuss announcing NEO discoveries.
New NEOs are announced to the world via the Minor Planet Center (MPC's) Circulars - in this case Minor Planet Electronic Circulars or MPECs. Each MPEC has a standard header and format, but each circular is unique in that it pertains to a different object to be announced. As an example, we will discuss the discovery announcement of 2018 KB3: www.minorplanetcenter.net/mpec/K18/K18KA1.html
At the top of each MPEC is the standard header providing some information on the MPC, contact information, and so on. Below this is the object designation (2018 KB3) followed by the observations in the standard format. Specified within the observation string is the exact time of each observation, the precise sky coordinates (in right ascension and declination), followed by the brightness of the object and finally the reference and reference location on the globe as indicated by the 3-character Observatory Code.
Below the observation block are specific observer details - showing which telescopes observed the object, and which observers took part in these observations. Further, there is information on the size and type of each telescope listed here.
Next follows the full orbital element set for each object. The orbital elements are used to project the location of the object, either in the past or future, to assist in searching for past observations or planning future observing. The orbital elements also allow the computation of the Earth MOID, which is the minimum distance between the orbit of the Earth and the current orbit of the object. MOIDs are useful for helping observers select which NEOs to target for future observations. In this case, a MOID of > 0.3 Astronomical Units (around 35 million miles) indicates that 2018 KB3 is not a threat to the Earth for the foreseeable future.
Beneath the orbital elements is what is called a residual block; this shows how well the observations published in this MPEC match the orbit the MPC computed. These residuals are all in *arcseconds*, or 1/3600 of a degree, for each right ascension and declination. These small numbers will indicate to those not familiar with observations just how precise NEO measurements are these days.
At the bottom of each MPEC is an ephemeris, or a list of future positions on the sky for 2018 KB3. It is placed here to assist observers in planning future observations of this object, if necessary. NEOs can appear just about anywhere in the sky, and change brightness rapidly, so the specifics of each object help guide observing planning.
With this as a general backdrop for interpreting an individual MPEC, the reader should know that last year (2017) the MPC issued over 2000 discovery MPECs! The message here is that NEO discoveries are made more or less daily, and most are entirely routine. Readers that wish to track the pace of discoveries, or simply browse all MPECs, can follow the two links below:
+ NEO Discovery Table: www.minorplanetcenter.net/iau/lists/YearlyBreakdown.html
+ Recent MPEC page: www.minorplanetcenter.net/mpec/RecentMPECs.html
2018 JB3 - The New Discovery of a Rare Atira-Class of NEO
(May 2018) On May 13, Richard Kowalski of the Catalina Sky Survey reported the discovery of a bright minor planet at the relatively small solar elongation of ~55 degrees. Astrometric follow-up from Tautenburg (033), Spacewatch II (291), Slooh Observatory, Canary Islands (G40), Great Shefford (J95), JAXA Space Tracking and Communications Center (P93); as well as prediscovery images from Palomar Mountain/ZTF (I41) allowed the MPC to perform precise orbital calculations.
As this Circular notes, 2018 JB3 has a trajectory that keeps the object closer to the Sun than the Earth at all times! This makes 2018 JB3 a special class of NEO - an Atira or Apohele object. This is only the 30th discovery of an object in this class.
The astute reader may wonder why we would be concerned about such objects from a threat perspective. After all, the orbit of this object fits snugly between the Earth and Sun, posing no immediate threat. While this is true, we do have several science and hazard-driven goals in studying such populations. First, this population is almost completely unknown. With only 30 discoveries, it is abundantly clear these are exceedingly difficult objects to discover from the ground and at the moment we really do not know how large the population might be. Second, objects on trajectories such as these are often unstable on 100-year timeframes, and minor changes to the orbit could render these objects potential impactors. Lastly, and perhaps most importantly, even among the 30 known objects in this class, there are a few that approach the Earth closely. Given the nature of the orbits, Atira objects often spend a lot of time in the vicinity of the Earth. This fact can render these objects a bit more likely to impact the Earth than other NEOs on an object-by-object basis. For a glance at the orbit of this object, readers may look at either the Minor Planet Center page or the JPL Center for NEO Studies page for this object. For a bit of background on early searches objects at small solar elongations, see research by David Tholen and Rob Whiteley from the late 1990s.