Orbit Properties

This page contains information about orbital properties of the object, as computed by the Aegis Orbit Determination and Impact Monitoring system. Orbital elements at a refence epoch are called osculating elements, and they describe an ellipse in the three-dimensional space. The reference frame used to compute these elements is the J2000 ecliptic reference frame. ASCII files containing the orbital data in Keplerian or Equinoctial elements can be downloaded using the buttons at the bottom of the webpage. Data shown here can be also automatically downloaded through HTTPS APIs, see instructions in Automated Data Access.

 

Epoch

Near present day. By activating this option, orbital elements computed near the present epoch are shown. This epoch is updated every 200 days.

Near middle of observation arc. By activating this option, orbital elements computed near the middle of the observation arc epoch are shown.   

Orbit properties

Epoch. Reference epoch at which the osculating orbital elements are computed, in Modified Julian Date (MJD).

Semimajor axis. Semimajor axis of the osculating ellipse. This parameter defines the size of the orbit.

Eccentricity. Eccentricity of the osculating ellipse. This parameter defines the shape of the orbit.

Inclination. Inclination of the osculating ellipse. This parameter defines the inclination of the asteroid orbital plane with respect to the horizontal plane of reference of the J2000 ecliptic reference frame.

Ascending Node. Ascending node of the osculating ellipse. This angle identifies the point at which the asteroid crosses the horizontal reference plane in ascending direction.

Arg. of Perihelion. Argument of perihelion of the osculating ellipse. This angle identifies the direction of the perihelion (see below) in the orbital plane of the asteroid.

Mean Anomaly. This angle identifies the position of the asteroid along the osculating ellipse.

Perihelion. Minimum distance from the Sun along the osculating ellipse.

Aphelion. Maximum distance from the Sun along the osculating ellipse.  

Asc. Node-Earth Sep. Distance from the asteroid orbit and Earth’s orbit at the ascending node.

Desc. Node-Earth Sep. Distance from the asteroid orbit and Earth’s orbit at the descending node.

MOID. Minimum Orbit Intersection Distance between the asteroid orbit and Earth’s orbit. This value represents the minimum separation between the orbit of the Earth and the ellipse of the asteroid orbit.

Orbit Period. Orbital period of the asteroid computed from the osculating orbital elements.

U parameter. Uncertainty parameter indicating the uncertainty of the orbit of the asteroid. It is a number from 0 to 9, where incremental values denote increasing uncertainty. More information on the definition can be found at the Minor Planet Center.

A1. Non-gravitational force along the radial direction, typically associated with the Solar Radiation Pressure, in 10-15 au/day2.

A2. Non-gravitational force along the tangent direction, typically associated with Yarkovsky effect, in 10-15 au/day2.

Covariance Matrix

The covariance matrix is a symmetric matrix containing information about the uncertainties of the orbital elements. From a statistical point of view, the orbit of an asteroid is a N-dimensional (with N = 6, 7, or 8) Gaussian probability with mean value equal to the nominal orbit, and covariance equal to the covariance matrix.

 

Physical Properties

Rotation Direction. Represents the direction of rotation of the asteroid, which can be either prograde (PRO) or retrograde (RETRO).

Taxonomy. Refers to the type of spectrometric classification of the asteroid. The search allows filtering by both Bus-DeMeo and Tholen taxonomy.

Absolute Magnitude (H). Absolute magnitude is a measure of brightness of the asteroid if that the object would have if it were one astronomical unit (AU) from both the Sun and the observer at a zero phase angle. It is expressed in absolute magnitudes (mag).

Slope Parameter (G). It is a parameter that quantifies the change in the absolute magnitude of an asteroid with the visual angle near opposition. It is expressed in magnitudes (mag).

Albedo. Albedo is a measure of an astronomical object's reflectivity, indicating how much light the object reflects. The value 0.14 is used by default.

Diameter. Refers to either the physical or the estimated diameter of the asteroid. This can be estimated based on absolute magnitude or measured using radar. In the case of asteroids with more than one spatial dimension associated with them, the search engine will return the asteroid even if only one of the 3 dimensions is within the search range. The default unit is meters (m).

Color Index Information. Represents the object's brightness through a set of specific wavelength filters. The user can set both the bands used to observe the asteroid and the limits of the asteroid's magnitude.

Spinvector L. Spinvector L represents the longitude component of the spin vector of an asteroid. It is a measure of the asteroid's rotation direction in degrees.

Spinvector B. Spinvector B represents the latitude component of the spin vector of an asteroid. It is a measure of the asteroid's rotation direction in degrees.

Rotation Period. Rotation period is the time it takes for an asteroid to complete one full rotation on its axis. It is measured in hours (h) by default.

Amplitude. Refers to the variation in an asteroid's brightness during its rotation. It is typically measured in magnitudes (mag) and indicates the difference in brightness between the brightest and dimmest points on the asteroid's surface.

Sightings. Sightings refer to the recorded instances of observing or tracking an asteroid's position and characteristics. It is a count of the number of times an asteroid has been observed or detected. 

 

Observations

The Observations tab includes the following information.

 

Observational Information

Arch Length. Number of days elapsed between the first observation collected for the object and the last observation.

Unobserved. Number of days elapsed since the last observation collected for the object and the last update date.

RMS of Residuals. Root mean square of the weighted observational residuals.

Astrometry Summary

First Observation. Date of the first astrometric observation.

Last Observation. Date of the last astrometric observation.

Total Optical Observations (Discarded). Total number of astrometric observations and, in parenthesis, number of discarded astrometric observations in the orbit determination process

Radar Summary

First Observation. Date of the first radar observation.

Last Observation. Date of the last radar observation.

Delay (Discarded). Total number of radar delay observations and, in parenthesis, number of discarded observations in the orbit determination process.

Doppler (Discarded). Total number of radar doppler observations and, in parenthesis, number of discarded observations in the orbit determination process.

Total Radar Observations (Discarded). Total number of radar delay and doppler observations and, in parenthesis, the total number of discarded radar observations in the orbit determination process.

 

Ephemerids

This page contains a service for the generation of the observational ephemerides of a given asteroid. The user must specify in each requested field: 1) the observatory from which the ephemerides need to be computed; 2) the initial date; 3) the final date; 4) the time step. This service is also available through the HTTPS APIs, see instructions in Automated Data Access. The request returns a text table to the user, with the following columns.

 

Date. The date in calendar format DD-MM-YY.

Hour (UTC). Hour in UTC time scale.

MJD (UTC). The date in Modified Julian Date format.  

RA (h m s). Equatorial J2000 right ascension angular coordinate, given in hours, minutes and seconds.

DEC (d ‘ ”). Equatorial J2000 declination angular coordinate, given in degrees, arc-minutes and arc-seconds.

Mag. Estimated visual magnitude of the object.

Alt (deg). Altitude over the observer local horizons in degrees. The value is meaningless for geocentric position (IAU Observatory Code = 500) and for space telescopes.  

Airmass. Airmass at the specified time. If the object is under the horizon, then this parameter is INF. The value is meaningless for geocentric position (IAU Observatory Code = 500) and for space telescopes.  

Sun elev. (deg). Sun elevation in degrees, that is the angle of the Sun over or under the horizon.  

SolEl (deg).  Solar elongation in degrees, that is the angle Sun-observer-asteroid.

LunEl (deg). Lunar elongation in degrees, that is the angle Moon-observer-asteroid.

Phase (deg). Phase angle in degrees, that is the angle Sun-asteroid-observer.

Glat (deg).  Galactic latitude in degrees.

Glon (deg). Galactic longitude in degrees.

R (au). Distance of the asteroid from the Sun in astronomical units.

Delta (au). Distance of the asteroid from the Earth in astronomical units.

RA*cosDE (“/min). Angular velocity in right ascension in arc-seconds per minute.

DEC (“/min). Angular velocity in declination in arc-seconds per minute.

VEL (“/min). Angular velocity in arc-seconds per minute.

PA (deg). Position angle in degrees.

Err1. The sky plane error describes the uncertainty of the prediction on the celestial sphere, represented by an ellipse. The error is composed by two quantities, giving the 1-sigma uncertainty along the major and the minor axes of the ellipse. Err1 represents the 1-sigma variation along the major axis, and it can be given in arc-seconds, arc-minutes, or degrees, depending upon its size.  

Err2. This value represents the 1-sigma variation along the minor axis, and it can be given in arc-seconds, arc-minutes, or degrees, depending upon its size.

AngAx (deg). Uncertainty ellipse position angle in degrees. This is the angle between the major axis of the uncertainty ellipse measured from North in counter clockwise direction.

 

Close Approaches

This table shows all the close encounters with the planets and the massive asteroids included in the dynamical model, from 1950 to 100 years in the future from the current epoch. A close approach is recorded when the distance is smaller than: 1) 0.2 au from the Earth; 2) 0.7 au from Jupiter, Saturn, Uranus, or Neptune; 3) 0.05 au from Mercury, Venus, or Mars; 4) 0.02 au from a massive asteroid. This table is also available through the HTTPS APIs, see instructions in Automated Data Access. The entries of the table are described below.

 

Body. It indicates the name of the body involved in the close approach.  

Date in UTC. Nominal date at which the minimum distance in reached.

Time uncert. in min. One-sigma uncertainty in the epoch of close approach, in minutes.

Nominal distance in au. Minimum distance from the reference body computed from the nominal orbit, in astronomical units.

Distance uncert. in au. One-sigma uncertainty in the close approach distance with the reference body

 

Possible Impacts

This table shows the possible impacting solutions (called Virtual Impactors) for which a non-zero impact probability has been computed. Virtual Impactors are searched for in the next 100 years in the future. If the object is included in the special risk list, then it shows impacting solutions from 100 years on. For these objects, the Torino Scale is not defined.

 

To understand the values in the Possible Impacts section, it is important to understand the concepts of Line Of Variations (LOV) and Target Plane (TP).

 

The LOV is a smooth curve in the fit parameters space, representing the largest uncertainty direction in the confidence region.

 

The TP is the plane passing through the centre of the Earth and orthogonal to the incoming asymptote of the hyperbola defining the two-body approximation of the trajectory at the time of closest approach. For each Virtual Impactor, the LOV is then represented in the TP.

 

This table is also available through the HTTPS APIs, see instructions in Automated Data Access. The entries of the table are described below.

 

Date in UTC. Calendar date in UTC at which the impact take place.

MJD. Modified Julian Date in UTC at which the impact take place.

σ. The approximate location along the LOV in sigma space. It measures how the impacting orbit is near the nominal. The value zero indicates the orbit is the nominal one.

σ_imp. The lateral distance in sigma-space from the LOV to the Earth's surface. The value zero indicates that the LOV passes through the Earth.

Distance ± Width in RE. The distance between the TP point corresponding to the Virtual Impactor and the Earth centre, together with the width (both in Earth radii).

Stretching in RE/σ. The stretching [units are in Earth radii scaled with the gravitational Earth radius, divided by sigma] is the semimajor axis of confidence region. It indicates how much the confidence region at the epoch has been stretched by the time of impact. This is inversely proportional to the impact probability.

In other words, it is a local quantity that roughly measures how much two points at unit distance in the σ parameter are separated when they are mapped to the TP. The higher is the stretching, the smaller is the number of points on the TP:

• When there are many points on the TP the stretching is small, and the geometry of the LOV is quite clear.
• On the contrary, when there is a strong non-linearity due to previous close approaches, the stretching is large and changes rapidly from point to point.

IP. Impact Probability of the corresponding Virtual Impactor.

Exp. energy. The expected energy, scaled with the impact probability, released at the impact, in MT of TNT equivalent. This is obtained by multiplying the kinetic energy and the Impact Probability.

PS. Palermo Scale. Further information about the estimation of the diameter can be found in Definitions & Assumptions.

TS. Torino Scale. Further information about the estimation of the diameter can be found in Definitions & Assumptions.

 

At the bottom of the table, additional information about the object is provided. The first line contains information about the number of observations used for the computation of the impact monitoring. The range of the impact cross section is also reported, and it is computed considering the gravitational focusing given by the gravity of the Earth. The LOV depends on the coordinates, and those used for the computation are reported in the following line. The last line shows the version of the software used and the date of computation.

 

rwo file

The <astname>.rwo file contains the observations and residuals of the corresponding asteroid. This file is also available through the HTTPS APIs, see instructions in Automated Data Access. The entries of the table are described below.

 

The file header is composed of a maximum of 5 lines. The first line contains the version of the rwo forma. The second line contains the error model in use. The third line contains the value of the RMS of the astrometric and radar post fit normalized residuals, if available. The following line contains the RMS of the photometric post fit normalized residuals, if available. The last line contains the expression ‘END OF HEADER’, which marks the end of the file header.

 

After the header, two comment lines are present. They start with the symbol ‘!’ and specify the content of the lines corresponding to optical observations. The following lines contain the optical observations, if available. A single astrometric measurement can occupy 1 or 2 lines, respectively for the case of an observation from the Earth and for the case of an observation from a satellite or a roving observatory.  

 

In case of a known fixed observatory on Earth, the measurement occupies one line. The line contains in this order:

1. The designation of the object.
2. The observation type and technology.  
3. A note on observation circumstances, corresponding to column 14 of the MPC 80col format.
4. The time fields, containing: the date in calendar format (YYYY, MM, DD) with the day expressed as a real number, followed by the time accuracy.
5. The right ascension fields, containing: the value expressed in hours, minutes and seconds; the accuracy; the a-priori formal RMS corresponding to the adopted error model; a flag to indicate if the weight assigned is manual or not (the flag is ‘T’ if the weight is manual, ‘F’ if it is assigned automatically by the software); the bias corresponding to the applied error model; the residual.  
6. The declination fields, containing: the value in degrees, minutes and seconds; the accuracy; the a-priori formal RMS, corresponding to the adopted error model; the flag telling if the weight assigned is manual or not; the bias corresponding to the applied error model; the residual.  
7. The magnitude fields, containing: the apparent magnitude value; the colour band; the a priori RMS; the residual.
8. The star catalogue used for astrometric reduction.
9. The station code.  
10. The chi-squared value of the observation residuals.
11. The selection flags for astrometry and photometry respectively. These flags are 0 if the observation is discarded, or 1 is the observation is used in the fit.

In case of an optical observation from a satellite, the measurement occupies two lines. The first line contains the angular measurements taken with respect to the satellite. The format is the same as above, but the observation type and technology have both value ‘S’. The second line contains the satellite position. This line contains the following fields:

1. The designation of the object.
2. The letters ‘S’ for observation type and ‘s’ for satellite position.
3. A note on observations circumstances, expressed by a single character string.
4. The time in calendar format.
5. The parallax unit: value ‘1’ for km and ‘2’ for AU.
6. The position of the satellite in equatorial coordinates.
7. The observer code.

The same format used for satellite observations is also used for roving observatory observations. In this case observation type is ‘O’ and the observer code is equal to ‘247’. The second line contains the observing site position in body fixed coordinates: East longitude, North latitude in radians and altitude in meters.

 

If present, radar observations are located at the end of the file, after the entire set of optical observations. Two comment lines beginning with ‘!’ denote the beginning of radar measurements. They specify the content of the lines corresponding to radar observations. A single measurement occupies one line, containing:

1. The designation of the object.
2. The observation type and technology. The letter ‘R’ is used for radar range and the letter ‘V’ is used for radar range rate. The technology value can be ‘c’ for measurement corrected for centre of mass, or ‘s’ for surface bounce.
3. A note on observational circumstances.
4. The time in calendar format.
5. Radar range in km or the range rate in km/d.
6. The measurement accuracy.
7. The a-priori RMS.
8. The flag for manual weight.
9. The bias.
10. The residual.
11. The transmitting and receiving station codes.
12. The chi-squared value.
13. The selection flag for the inclusion in the fit.

 

Orbit files

Orbit files are provided in two different sets of orbital elements: Keplerian or Equinoctial. Keplerian elements are defined as: semimajor axis (a), eccentricity (e), inclination (i), longitude of the ascending node (Ω), argument of perihelion (ω), and mean anomaly (M). Equinoctial elements are typically referred with symbols a, h, k, p, q, M, where a is the semimajor axis and M is the mean anomaly. The other elements are obtained through the following relations:

 

h = e sin(Ω + ω); k = e cos(Ω + ω); p = tan(i/2) sin(Ω); q = tan(i/2) cos(Ω)

 

Orbital elements are provided either near the current epoch, or near the middle epoch of the observational arc.  The file formats of the orbits are inherited from the OrbFit software.

 

The files with Equinoctial elements ( <astname>.eq0 or <astname>.eq1) have the following structure:

1. A 4-line header containing details of the file format and the reference system.
2. The END_OF_HEADER expression.
3. The name of the object.
4. A comment on the type of orbital elements provided.
5. A line starting with the string ‘EQU’ and followed by the nominal values of the orbital elements.
6. A line starting with the string ‘MJD’ and followed by the epoch at which the orbital elements are determined.
7. A line starting with the string ‘MAG’ and followed by the values of the absolute magnitude H and the slope parameter G.
8. A comment on the non-gravitational parameters used for the determination of the orbit.  
9. A line starting with the string ‘LSP’ followed by three integer values:
   1. The first one is: 0 if only the gravitational model is used; 1 if a non-gravitational model including the Yarkovsky effect and/or the direct solar radiation pressure effect are used.
   2. The second one is the number of parameters in use, which can be 0, 1, or 2
   3. The third one is the dimension of the parameter space, which is 6 plus the number of dynamical parameters determined in the orbital fit.
10. If non-gravitational effects are used, a line starting with the string ‘NGR’ containing the values of the solve for parameters. The area-to-mass ratio is expressed in m2/ton, while the parameter A2 for the Yarkovsky effect is in 10-10 au/day2.
11. A line starting with the string ‘! RMS’ containing the 1-sigma uncertainties of the determined parameters, including the non-gravitational ones.
12. A line starting with the string ‘! EIG’ containing the square roots of the eigenvalues of the covariance matrix.
13. A line starting with “! WEA’ containing the weak direction vector, i.e. the eigenvector corresponding to the smallest eigenvalue.
14. The lines beginning with ‘COV’ contain the upper triangular part of the covariance matrix of the orbit determination. If 6, 7, 8, 9 or 10 parameters are determined, there are respectively 7, 10, 12, 15 or 19 COV lines, containing three scalar values each (except possibly the last line). Values are ordered by rows.
15. The lines beginning with ‘NOR’ contain the upper triangular part of the normal matrix of the orbit determination. The format is the same as for the covariance matrix, with the same number of lines. For both the covariance and normal matrices, the units for distances are astronomical units and the units for angles are degrees.

The files with Keplerian elements ( <astname>.ke0 or <astname>.ke1) have the following structure:

1. A 4-line header containing details of the file format and the reference system.
2. The END_OF_HEADER expression.
3. The name of the object.
4. A comment on the type of orbital elements provided.
5. A line starting with the string ‘KEP’ and followed by the nominal values of the orbital elements. The units for distances are in astronomical units, and the units for angles are degrees.
6. A line starting with the string ‘MJD’ and followed by the epoch at which the orbital elements are determined.
7. A line starting with the string ‘MAG’ and followed by the values of the absolute magnitude H and the slope parameter G.
8. A comment on the non-gravitational parameters used for the determination of the orbit.
9. A line starting with the string ‘LSP’ followed by three integer values:
   1. The first one is: 0 if only the gravitational model is used; 1 if a non-gravitational model including the Yarkovsky effect and/or the direct solar radiation pressure effect are used.
   2. The second one is the number of parameters in use, which can be 0, 1, or 2
   3. The third one is the dimension of the parameter space, which is 6 plus the number of dynamical parameters determined in the orbital fit.
10. If non-gravitational effects are used, a line starting with the string ‘NGR’ containing the values of the solve for parameters. The area-to-mass ratio is expressed in m2/ton, while the parameter A2 for the Yarkovsky effect is in 10-10 au/day2.
11. A line containing the perihelion distance, in astronomical units, beginning with ‘! PERIHELION’.
12. A line containing the aphelion distance, in astronomical units, beginning with ‘! APHELION’.
13. A line containing the ascending nodal distance, in astronomical units, beginning with ‘! ANODE’.
14. A line containing the descending nodal distance, in astronomical units, beginning with ‘! DNODE’.
15. A line containing the value of the MOID with the Earth, in astronomical units, beginning with ‘! MOID’.
16. A line containing the value of the orbital period, in days, beginning with ‘! PERIOD’.
17. A line indicating whether the object is a Potentially Hazardous Object of not, beginning with ‘! PHA’.
18. A line containing the velocity at infinity with respect to the Earth in km/s, beginning with ‘! VINFTY’.
19. A line containing the MPC uncertainty parameter, beginning with ‘! U_PAR’.
20. A line containing the NEO class among Atira, Aten, Apollo, and Amor, beginning with ‘! ORB_TYPE’.
21. A line starting with the string ‘! RMS’ containing the 1-sigma uncertainties of the determined parameters, including the non-gravitational ones.
22. The lines beginning with ‘COV’ contain the upper triangular part of the covariance matrix of the orbit determination. If 6, 7, 8, 9 or 10 parameters are determined, there are respectively 7, 10, 12, 15 or 19 COV lines, containing three scalar values each (except possibly the last line). Values are ordered by rows.
23. The lines beginning with ‘COR’ contain the upper triangular part of the correlation matrix of the orbit determination. The format is the same as for the covariance matrix, with the same number of lines. For both the covariance and correlation matrices, the units for distances are astronomical units and the units for angles are degrees.