sphunif (version 1.4.3)

comets: Comet orbits

Description

Comet orbits data from the JPL Small-Body Database Search Engine. The normal vector of a comet orbit represents is a vector on \(S^2\).

Usage

comets

Format

A data frame with 3798 rows and 13 variables:

id

database ID.

spkid

object primary SPK-ID.

full_name

full name/designation following the IAU naming convention.

pdes

object primary designation.

frag

flag indicating if the record is a comet fragment.

diameter

diameter from equivalent sphere (in km).

i

inclination; the orbit's plane angle with respect to the ecliptic plane, in radians in \([0, \pi]\).

om

longitude of the ascending node; the counterclockwise angle from the vector pointing to the First Point of Aries and that pointing to the ascending node (the intersection between orbit and ecliptic plane), in radians in \([0, 2\pi)\). (Both vectors are heliocentric and within the ecliptic plane.)

per_y

sidereal orbital period (in years).

class

orbit classification. A factor with levels given below.

e

eccentricity of the orbit.

a

semi-major axis of the orbit (in AU).

w

argument of perihelion; the (shortest) angle between the vector pointing to the ascending node and that pointing to the perihelion (nearest orbit point to the Sun), in radians in \([0, \pi]\). (Both vectors are heliocentric and within the orbit's plane.)

first_obs, last_obs

Date of the first and last recorded observations used in the orbit fit.

ccf09

flag indicating if the comet was considered in the data application in Cuesta-Albertos et al. (2009); see details below.

Details

The normal vector to the ecliptic plane of the comet with inclination \(i\) and longitude of the ascending node \(\omega\) is $$(\sin(i) \sin(\omega), -\sin(i) \cos(\omega), \cos(i))'.$$

A prograde comet has positive \(\cos(i)\), negative \(\cos(i)\) represents a retrograde comet.

class has the following levels:

• COM: comet orbit not matching any defined orbit class.

• CTc: Chiron-type comet, as defined by Levison and Duncan (T_Jupiter > 3; a > a_Jupiter).

• ETc: Encke-type comet, as defined by Levison and Duncan (T_Jupiter > 3; a < a_Jupiter).

• HTC: Halley-type comet, classical definition (20y < P < 200y).

• HYP: comets on hyperbolic orbits.

• JFc: Jupiter-family comet, as defined by Levison and Duncan (2 < T_Jupiter < 3).

• JFC: Jupiter-family comet, classical definition (P < 20y).

• PAR: comets on parabolic orbits.

Hyperbolic and parabolic comets are not periodic; only elliptical comets are periodic.

The ccf09 variable gives the observations considered in Cuesta-Albertos et al. (2009) after fetching in the database in 2007-12-14 for the comets such that !(class %in% c("HYP", "PAR")) & per_y >= 200. Due to the dynamic nature of the data, more comets were added to the database since 2007 and also some past records were updated.

The script performing the data preprocessing is available at comets.R. The data was retrieved on 2022-05-28. A previous version of this dataset based on the old NASA's JPL Database (accessed on 2020-05-07) is available at comets-old.rda and was obtained with comets-old.R.

References

Cuesta-Albertos, J. A., Cuevas, A., Fraiman, R. (2009) On projection-based tests for directional and compositional data. Statistics and Computing, 19:367--380. tools:::Rd_expr_doi("10.1007/s11222-008-9098-3")

Examples

# Load data
data("comets")

# Add normal vectors
comets$normal <- cbind(sin(comets$i) * sin(comets$om),
                       -sin(comets$i) * cos(comets$om),
                       cos(comets$i))

# Tests to be performed
type_tests <- c("PCvM", "PAD", "PRt")

# Excluding the C/1882 R1-X (Great September comet) records with X = B, C, D
comets_ccf09 <- comets[comets$ccf09, ][-c(13:15), ]

# Sample size
nrow(comets_ccf09)

# Tests for the data in Cuesta-Albertos et al. (2009)
tests_ccf09 <- unif_test(data = comets_ccf09$normal, type = type_tests,
                         p_value = "asymp")
tests_ccf09