mpcorb database: its properties and use in Guide and Charon

What mpcorb is: mpcorb is a database of asteroid orbits maintained by the Minor Planet Center. It gives orbits for all numbered and observable unnumbered asteroids, and is available at Mirror sites exist (but have not been updated since February 2010):

 Klet Observatory,  Czech Republic 
 Lulin Sky Survey,  Taiwan with username mpcorb and password Ceres. 

but note that only the first two seem to have been updated recently! Check file dates before downloading!

Other mirror sites may be mentioned on the MPC's own page about mpcorb.

Before their Web site was hacked in February 2010, MPC provided the main database in two forms: as mpcorbcr.dat and mpcorb.dat. Now, only the latter is available. Both contained exactly the same data, but the former was in PC format (with a carriage return/line feed at the end of every line of data), the latter in Unix format (a line feed but no CR at the end of each line). Guide and Charon and some other software will recognize either file. mpcorb.txt is available in .ZIP format, reducing the download size considerably, to about 30 MBytes. The files are updated daily.

Some people have run into troubles in accessing this data from the MPC site. If you're one of them, click here. (It's hoped that the mirror sites will reduce this trouble.)

A little utility program for manipulating mpcorb: mpcorb is now available only in the Unix form; i.e., mpcorbcr is no more. Also, I sometimes find myself needing an mpcorb file with only certain objects in it: perhaps those with perihelia less than 1.3 AU, or with H<7, or maybe both criteria at once. I've written a little utility, mpcorbx, to do this sort of filtering, and/or convert from the UNIX line-feed form to the DOS CR/LF form.

Use of mpcorb.dat in Guide: To use the datasets in Guide, move either the mpcorb.dat or mpcorbcr.dat file into the Guide directory. The Extras menu in Guide has an option, "Use mpcorb", shut off by default. (If it is grayed out, it means that Guide can't find either .dat file.) When you use the toggle, Guide will swap to use of mpcorb data.

If you wish to set Guide 8.0 or 9.0 to use an mpcorb.dat file from a folder such as (for example) c:\asteroid_data, you would hit Alt-J and enter


If you have a file of asteroid data in the same format as mpcorb.dat, but its name is (for example) c:\asteroid_data\my_asteroids.txt, you would hit Alt-J and enter


If you later wanted to go back to using Guide's 'built in' mpcorb.dat, you would hit Alt-J and enter


Use of mpcorb in Guide has its pros and cons. Foremost among the advantages of mpcorb is that it is completely up to date, reflecting the latest orbits computed by the Minor Planet Center. Guide disks are up-to-date at the time they are made, but even while they are in production, new objects are being found and old ones are having their orbits improved via new observations. This won't matter much if you're looking at brighter asteroids that already have very well-determined orbits, but becomes quite important if you want to observe fainter, more recently discovered objects.

Click here for information about use of mpcorb with Charon.

There are a few disadvantages to use of mpcorb . The data exists at only one epoch, always within 100 days of the present. If you try to compute positions far away from that epoch, the quality of the results will gradually deteriorate. The Guide CD provides orbital elements at 50-day intervals over a span of several decades, so the epoch of the data is never off by more than 25 days. Thus, for objects that were well-determined in the original Guide data, mpcorb positions will be less accurate. It's best to avoid mpcorb , for example, in computing asteroid occultations, which always involve well-determined objects. (This is in no way MPC's fault, though. If Guide had a built-in orbital integrator, this problem would go away and MPC would be more accurate in all cases.)

You can evade this problem through the use of the integrat software, described and downloadable here. This software can read any file in the mpcorb format and integrate it to a desired epoch.

Also, be warned that use of mpcorb in Guide can be slow. Each time you go outside a particular 50-day span, Guide has to compute some basic data as to where the asteroid will be over that time span. day. This speeds up subsequent drawing, since it enables Guide to discard about 99% of the asteroids as "off-screen" for a given chunk of sky. But, at least when you change Guide's date/time to go outside the current span, there will be a delay of some seconds while the recomputing is done.

In any case, if mpcorb.dat or mpcorbcr.dat are available to Guide, then when you click for "more info" on an asteroid, some comments from mpcorb will be given.

Some people are apt to wonder why this database is used instead of the Lowell Observatory ASTORB dataset. mpcorb has several advantages over ASTORB. mpcorb contains currently visible objects; ASTORB contains a lot of objects that were observed briefly, long ago, and which are essentially "lost" now. mpcorb tends to be slightly more up to date (understandable, since ASTORB is based on waiting for MPC data to arrive). At some point, I may revise Guide to work with either dataset. But it does appear that mpcorb is best suited to the use of observers; this was my primary goal.

astorb to mpcorb converter: I've written a little piece of code that will read in astorb.dat and write out the data into mpcorb.dat, doing a suitable format conversion. You can click here to download the converter (Win32 .exe and .cpp source code).

Under Linux and other non-Windows systems, you can compile the source code easily enough; directions are given at the top of the .cpp file.

Then just run ast2mpc, and it'll tell you how many objects are in the input file, and write out the converted mpcorb.dat file, giving a percentage progress report as it goes. Note that the output will have blank fields for references, number of oppositions, orbit arc, root-mean-square error, and date last observed. Those fields are missing in astorb, so there's no decent way to translate them into the mpcorb format. Also, the perturber field is a little bit inaccurate: in addition to handling all the perturbers mentioned, astorb also includes a few small asteroid perturbers ignored by MPC. (astorb includes (1) Ceres, (2) Pallas, (4) Vesta, (10) Hygiea, and (15) Eunomia, and that fact can be described in the mpcorb format; but astorb also includes (52) Europa, (511) Davida, and (704) Interamnia, and there's no way to mention this in the mpcorb format.)

However, names, magnitude data, and orbital elements and most other data will be translated accurately, and I think this converter will work for almost all purposes.

Problems in accessing the mpcorb data (and the Minor Planet Center site in general): Some people who attempt to access the mpcorb data will get an error such as "FTP Error - Could not login to FTP server". That's a result of some efforts made at MPC to deter hackers, spammers, and other vermin.

The simplest way around these issues is to use a mirror site instead of the MPC one. If you're really gung-ho about use of the MPC site, then here are the two things to check:

(1) As is now described partway down the MPC's main page, anonymous ftp passwords are now checked:

You must also ensure that you have set your anonymous ftp password in
your browser. This password must contain the "@" character. The default
values for this setting in browsers such as Netscape and Mozilla will
NOT work. (New requirement 2003 Aug. 27)

In Internet Exploder, one should use Tools... Internet Options, click on Content tab, and then on the My Profile button. You can then select the "Name" tab, then the "Edit" button, after which one can finally edit it to provide some different e-mail address.

In Mozilla, and probably in Netscape, one should click on the Edit... Preferences dialog, then on Advanced. This will give a "Send this e-mail address as anonymous FTP password".

In both cases, one can provide a garbage e-mail address; it doesn't appear that MPC requires that the address be legitimate.

(2) The following post on the Minor Planet Mailing List gives the gory details on some of the other security precautions taken by MPC. Those concerning anonymous ftp are relevant here:

From: "Gareth V. Williams"
Subject: {MPML} Accessing mpcorb 

Following a number of enquiries on this mailing list and via e-mail, I
shall summarise the security checks used to determine whether access to
computers here at the CfA is permitted.

(1) E-mail

  Two checks are made with incoming e-mail:

  (a) Does the e-mail originate from a site on the spammer blacklist?
If so, bounce the message.

  (b) Do a reverse DNS check on the site from which the e-mail originates.
     Is it properly DNS registered?  If not, bounce message.

(2) http

  No checks are made since Web access is only browsing.

(3) anon-ftp

  Do a reverse DNS on the requesting site.  If not properly
registered, refuse connection.

  The problems a number of you have been reporting are almost
certainly due to the fact that your ISP is not properly registering
its machines. Note that is not sufficient that the outgoing request
contain either the machine's IP address or host name (or both): the
machines here must be able to quiz a DNS host to convert the address
to the name (or vice versa).  It is up to the ISP to properly ensure
that all their hosts are properly registered.

  These checks are security measures to try and ensure that all
communications can be tracked back to their (valid) source.  This
is especially important with the recent increase in attacks on
high-profile sites.  You'd be surprised how often hacking attempts
are made on the machines on the Harvard network (including one very
successful attempt on some CfA U**x machines a year or two back).
But, then again, maybe you wouldn't (:-)

Gareth V. Williams, MS 18, 60 Garden Street, Cambridge, MA 02138, U.S.A.
Associate Director, IAU Minor Planet Center
E-mail address suppressed 
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