The collision of the Little Red Spot and Great Red Spot: Part 2
collision of the Little Red Spot and Great Red Spot: Part 2
H. Rogers, British
early July, the South Tropical Little Red Spot (LRS) (or Baby Red Spot, as NASA
have nick-named it) collided with the Great Red Spot (GRS) and was shredded by
its vigorous winds. Our earlier
report, produced on July 15, described the initial events.
This report fills in further details of that initial collision, and
continues the story up to early August. Starting
on July 2, the LRS seems to have been pulled into two main parts, the leading
part marked by several bright spots orbiting rapidly on the rim of the
GRS, and the trailing part -- the main remnant of the LRS – re-emerging
preceding (p.) the GRS. HST images
on July 8.9 showed these parts were still connected, forming a spiral completely
encircling the GRS. The remnant E
of the GRS drifted N and then W, colliding with the GRS again on July 16.
Images from July 17 to 25 showed probable remnants of it orbiting slowly
around the north side of the GRS. Only
one distinct product of these events survives: a dark streak which emerged from
the GRS rim following the LRS remnant, and continued prograding to the E.
However, there may be persistent smaller-scale effects both within and preceding
extra images have been received showing important stages in the earlier events (Figure
4). They include images by
Paul Maxson on July 2 – the first to show stretching and disruption of the LRS
as it was swept around the GRS – and July 9 – the last to show definite
reddish colour in the pale ‘LRS remnant’ that had emerged p. the GRS. They also include the publicly released Hubble Space Telescope
(HST) image on July 8.9 (credit NASA, ESA, and Dr. Amy Simon-Miller of GSFC).
HST image dramatically confirms the link between the two products of the LRS
disruption that we reported earlier: first, a string of 2 or 3 white spots
orbiting in the N rim of the GRS on July 4-6, and then, the more conspicuous LRS
remnant emerging p. the GRS on July 5-6 (Figure 5).
The HST image on July 8.9 shows that the latter remnant was indeed a
coherent, but highly distorted oval with streaks of orange colour; but this was
connected to a bright lane forming a 360-degree spiral all the way round the GRS
to a white spot inside its rim. This
spiral probably represented the complete LRS, disrupted on July 2 and pulled
into a loop all around the GRS! This
is shown by labelled images (Figure 5) and
position angle measurements (Figure 6). The
LRS portion closest to the GRS was dragged into and around it with a period of
~5 days, and the white spots imaged by amateurs on July 4-6 represented either
this portion or further disturbance arising around it. (The PA measurements
indicate a range of speeds, so some spots may have been transient, and the HST
image also shows a disturbed sector within the GRS ahead of the tip of the
the portion of the LRS further from the GRS squeezed round its S edge and
re-formed into the ‘LRS remnant’ on its p. side.
We can now describe the further fate of this feature (Figures
7 & 9) *[footnote].
On July 7-8 it was a pale orange, methane-bright spot, prograding away
from the GRS. On July 10-12, the
orange tint had faded away but the remnant was still perceptible as a bright
spot (at the p. end of a very dark streak extending out from the GRS rim). It
halted at L2 = 108 (possibly merging with a pre-existing retrograding white
spot). On July 13-14 it moved northwards, becoming slightly reddish again, and
then headed back towards the GRS. Meanwhile on July 10-14 the methane-bright
area was more extended, and covered both the bright spot, and the p. end of the
dark streak which continued to prograde. On
July 15 the methane-bright spot seemed to lie on the boundary between the two.
Thereafter, amateur images showed no remaining methane-bright material
(July 19 onwards).
LRS remnant came back to collide with the GRS again on July 16.
It was probably recorded as a tiny white spot drifting around the Red
Spot Hollow on July 17-18 (with another similar spot ahead of it) (Figure
8). The drift rate was remarkably slow, equivalent to a period of ~15
days (Fig.6, spot 4). By July 19, it ended up
in the larger, semi-permanent white spot complex at the northernmost point of
the Red Spot Hollow, and that seemed to be the end of the story. However, 3 days later, a white spot with dark rim broke out
from this complex and continued retrograding around the Red Spot Hollow (nominal
period ~17.5 days, or possibly a pair of spots travelling faster: Figs.6
& 8). This unusually
well-defined spot, at the head of a notable dark blue-grey sector of GRS rim,
may well have been the last distinct appearance of the LRS remnant.
It was last seen on July 25 as it approached the f. (W) end of the GRS,
where retrograding spots usually disappear.
the region p. the GRS was a rather chaotic scene of dark streaks and a few tiny
bright spots (Figure 8), but I suspect that
little of this was due to the LRS collision, although small-scale clouds or
vortices from the LRS might well have spread into this region below our level of
resolution. Features indicated on Figures 8 & 9
arrow): The one definite persisting outcome was the prograding dark spot that
originally marked the p. end of the dark streak that emerged with the LRS
remnant: DL2 = -3 deg/day.
(Purple arrowhead): A conspicuous bright spot at L2 ~ 102 (July 12-21) existed
beforehand, but its retrograding
drift was halted as it encountered the prograding dark streak (as well as a
faster-retrograding SEBs white spot); thus it may have been influenced
indirectly by the LRS disruption. At
this time it became a distinct reddish oval (July 17-20). It may be the same
reddish oval, reappearing from the surrounding murk, that was recorded closer to
the GRS (L2 = 107) on July 29-30.
arrowheads): Tiny white spots retrograding among the dark streaks (DL2 ~ +3
deg/day) and entering the Red Spot Hollow.
The LRS Remnant had joined this column, but the others were probably
GRS may still be showing effects of the LRS collision. Its increase in longitude
from L2 = 125 to 128.5 is more than expected from the usual 90-day oscillation,
and may well be a reaction to the collision. Its
appearance on July 29-30 was still quite unusual: note a very dark blue-grey
spot retrograding around the Hollow, another dark blue-grey rim section trailing
behind it, and an orange annulus within the northern rim of the GRS, separated
from the dark GRS core by a white strip. Thus, small-scale disturbance may
continue for a little while.
- - - - - - - -
were pre-existing spots in northern STropZ: a band of dark streaks, with white
bays becoming evident as they neared the GRS (including the one marked purple on
the figures), all moving with DL2 = +1 deg/day.
Just north of this band, there were some tiny white spots in SEBs with
DL2 = +3 deg/day (including the ones marked green on the figures).
- - - - - - -
continued from previous report):
(South is up in all images. Click for full size versions.)
more images from earlier stages of the events.
images showing how the multiple LRS remnants seen in amateur images relate to
the 360-deg. spiral seen in the HST image.
The LRS is stretched continuously from July 2 onwards, until July 8.9
when it forms a noose completely encircling the GRS.
of position angle (PA) of white spots orbiting around the GRS (continued from
Fig.3b). For these measurements, the images were stretched to make the GRS
approximately circular (as in Fig.5), and the PA of white spots was measured
from south towards east.
from July 11-15, showing the extended methane-bright region, while the LRS
remnant light spot (red arrow) drifted north and headed back towards the GRS.
The p. end of a dark streak from the GRS rim (blue arrow) continued
of the best images, July 14 to August 3, with spots colour-coded.
Methane images are not included as no methane-bright remnant was
detectable after July 15.
of the GRS, LRS remnant, and adjacent spots (measured by JHR).
Jupiter Section Director,
British Astronomical Association.