View source for Alinda asteroid

{{Short description|Group of near-Earth asteroids}}
The '''Alinda asteroids''' are a [[List of minor-planet groups|dynamical group]] of [[asteroid]]s with a [[semi-major axis]] of about 2.5 [[Astronomical unit|AU]] and an [[eccentricity (orbit)|orbital eccentricity]] approximately between 0.4 and 0.65.<ref>[http://www.projectpluto.com/mp_group.htm Minor planet groups/families] {{webarchive|url=https://web.archive.org/web/20101128141616/http://projectpluto.com/mp_group.htm |date=2010-11-28 }}</ref> The namesake is [[887&nbsp;Alinda]], discovered by [[Max Wolf]] in 1918.

These objects are held in this region by the 3:1 [[orbital resonance]] with [[Jupiter]] (2.502 AU), which results in their being close to a 1:4 resonance with [[Earth]] (2.520 AU). An object in this resonance has its orbital eccentricity steadily increased by gravitational interactions with Jupiter until it eventually has a close encounter with an [[inner planet]] that breaks the resonance.

Some Alindas have [[perihelion|perihelia]] very close to [[Earth]]'s orbit, resulting in a series of close encounters at almost exactly four-year intervals, due to the 1:4 near resonance.

One consequence of this is that if an Alinda asteroid happens to be in an unfavorable position for viewing at the time of its close approach to Earth (for instance, at a small elongation from the [[Sun]]), then this situation can persist for decades.  Indeed, as of 2010, the Alinda asteroid [[1915&nbsp;Quetzálcoatl]] had been observed only once since 1985.

Another consequence is that some of these asteroids make repeated relatively close approaches to Earth, making them good subjects for study by Earth-based [[radar]]. Examples are [[4179&nbsp;Toutatis]] and [[6489&nbsp;Golevka]], as well as [[2019&nbsp;MO]], which impacted Earth in June 2019.

== Dynamic age ==
The 3:1 resonance with Jupiter causes a repeating growth in the eccentricity of the asteroid's orbit. Dynamically young members have an eccentricity ranging from about 0.30 to 0.34 staying mostly in the [[asteroid belt]] ranging 1.7–3.4 AU from the Sun.<ref name="Lewis"/> Older members such as 8709 Kadlu have an eccentricities between 0.465 and 0.475 and cross the orbit of [[Mars]]. (8709 Kadlu makes approaches close enough to Jupiter, Mars, and Earth to be gravitationally nudged.)<ref name="Kadlu"/> The oldest members with eccentricities between 0.57 and 0.75 cross the orbit of Earth.<ref name="Lewis"/> [[3360 Syrinx]] is the most eccentric of the Alinda group with an eccentricity of 0.7 and the orbit has a dynamically short life expectancy.

== List of members ==

{| class="wikitable sortable" style="font-size: 89%; float: left; margin-right: 1em;"
! width=150 | [[Minor planet designation|Designation]] !! width=90 | ''[[Semimajor axis|a]]'' !! width=90 | ''[[eccentricity (orbit)|e]]'' !! width=90 class="unsortable" | Refs
|-
| '''[[887 Alinda]]''' || 2.48422 || 0.56356 || {{JPL|887}}{{·}}{{MPC|887}}
|-
| '''[[1429 Pemba]]''' || 2.55185 || 0.33858 || {{JPL|1429}}{{·}}{{MPC|1429}}
|-
| '''[[1550 Tito]]''' || 2.54673 || 0.30984 || {{JPL|1550}}{{·}}{{MPC|1550}}
|-
| '''[[1607 Mavis]]''' || 2.54783 || 0.30741 || {{JPL|1607}}{{·}}{{MPC|1607}}
|-
| '''[[1915 Quetzálcoatl]]''' || 2.54207 || 0.57170 || {{JPL|1915}}{{·}}{{MPC|1915}}
|-
| '''[[2608 Seneca]]''' || 2.5035 || 0.57620 || {{JPL|2608}}{{·}}{{MPC|2608}}
|-
| '''[[3360 Syrinx]]''' || 2.46803 || 0.74295 || {{JPL|3360}}{{·}}{{MPC|3360}}
|-
| '''[[3628 Božněmcová]]''' || 2.53691 || 0.30052 || {{JPL|3628}}{{·}}{{MPC|3628}}
|-
| [[3806 Tremaine]] || 2.54058 || 0.31301 || {{JPL|3806}}{{·}}{{MPC|3806}}
|-
| '''[[4179 Toutatis]]''' || 2.51005 || 0.63423 || {{JPL|4179}}{{·}}{{MPC|4179}}
|-
| [[5847 Wakiya]] || 2.54442 || 0.30086 || {{JPL|5847}}{{·}}{{MPC|5847}}
|-
| [[5864 Montgolfier]] || 2.55866 || 0.32007 || {{JPL|5864}}{{·}}{{MPC|5864}}
|-
| [[6318 Cronkite]] || 2.51002 || 0.46522 || {{JPL|6318}}{{·}}{{MPC|6318}}
|-
| [[(6322) 1991 CQ]] || 2.51628 || 0.47349 || {{JPL|6322}}{{·}}{{MPC|6322}}
|-
| '''[[6489 Golevka]]''' || 2.50768 || 0.60382 || {{JPL|6489}}{{·}}{{MPC|6489}}
|-
| '''[[(6491) 1991 OA]]''' || 2.50959 || 0.58946 || {{JPL|6491}}{{·}}{{MPC|6491}}
|-
| '''[[7092 Cadmus]]''' || 2.52493 || 0.70202 || {{JPL|7092}}{{·}}{{MPC|7092}}
|-
| [[7345 Happer]] || 2.45047 || 0.32467 || {{JPL|7345}}{{·}}{{MPC|7345}}
|-
| {{LoMP|7568|{{mp|(7568) 1988 VJ|2}}}} || 2.52739 || 0.33216 || {{JPL|7568}}{{·}}{{MPC|7568}}
|-
| [[(7569) 1989 BK]] || 2.54950 || 0.30348 || {{JPL|7569}}{{·}}{{MPC|7569}}
|-
| '''[[7638 Gladman]]''' || 2.53634 || 0.31606 || {{JPL|7638}}{{·}}{{MPC|7638}}
|-
| '''{{mpl|(8201) 1994 AH|2}}''' || 2.53362 || 0.70851 || {{JPL|8201}}{{·}}{{MPC|8201}}
|-
| [[8709 Kadlu]] || 2.53497 || 0.48432 || {{JPL|8709}}{{·}}{{MPC|8709}}
|-
| [[(9047) 1991 QF]] || 2.52479 || 0.31661 || {{JPL|9047}}{{·}}{{MPC|9047}}
|}
{{clear}}

== See also ==
{{div col|colwidth=20em}}
* [[Amor asteroid]]
* [[Apollo asteroid]]
* [[Aten asteroid]]
{{div col end}}

== References ==
{{reflist|refs=

<ref name="Lewis">{{cite web
 |title=The Alinda Family of Asteroids
 |author=John S Lewis
 |date=2015-08-03
 |url=http://www.johnslewis.com/2015/08/the-alinda-family-of-asteroids.html
 |accessdate=2019-06-26}}</ref>

<ref name="Kadlu">{{cite web
  |title=JPL Small-Body Database Browser: 8709 Kadlu (1994 JF1)
  |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=8709;cad=1#cad
  |publisher  = [[Jet Propulsion Laboratory]]
  |accessdate = 2019-06-26}}</ref>

}} <!-- end of reflist -->

{{Small Solar System bodies}}

[[Category:Alinda asteroids|*]]
[[Category:Asteroid groups and families]]