Editing Giotto (spacecraft) (section)

==Scientific results==

Images showed Halley's nucleus to be a dark peanut-shaped body, 15&nbsp;km long, 7&nbsp;km to 10&nbsp;km wide. Only 10% of the surface was active, with at least three outgassing jets seen on the sunlit side. Analysis showed the comet formed 4.5 billion years ago from volatiles (mainly ice) that had condensed onto interstellar dust particles. It had remained practically unaltered since its formation.

Measured volume of material ejected by Halley:

* 80% [[water]],
* 10% [[carbon monoxide]]
* 2.5% a mix of [[methane]] and [[ammonia]].
* other [[hydrocarbon]]s, [[iron]], and [[sodium]] were detected in trace amounts.

''Giotto'' found Halley's nucleus was dark, which suggested a thick covering of dust.<ref name="esa">{{cite web|title=ESA Science & Technology: Halley |publisher=[[ESA]] |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31878 |date=10 March 2006 |access-date=22 February 2009}}</ref>

The nucleus's surface was rough and of a porous quality, with the density of the whole nucleus as low as 0.3 g/cm<sup>3</sup>.<ref name="esa" /> Sagdeev's team estimated a density of
0.6 g/cm<sup>3</sup>,<ref name="density">{{Cite journal|title=Is the nucleus of Comet Halley a low density body?|volume= 331|issue= 6153|pages= 240|author= RZ Sagdeev|author2= PE Elyasberg|authorlink2=Pavel Elyasberg|author3= VI Moroz|journal=Nature|bibcode=1988Natur.331..240S|year=1988|doi= 10.1038/331240a0|s2cid= 4335780}}</ref> but S. J. Peale warned that all estimates had error bars too large to be informative.<ref name="Peale">{{cite journal |title=On the density of Halley's comet |author=S. J. Peale |journal=[[Icarus (journal)|Icarus]] |volume=82 |issue=1 |pages=36–49 |date = November 1989|doi=10.1016/0019-1035(89)90021-3 |bibcode=1989Icar...82...36P}}</ref>

The quantity of material ejected was found to be three tonnes per second<ref name="mcd">{{cite journal |title=Dust density and mass distribution near comet Halley from Giotto observations |author=J. A. M. McDonnell |display-authors=etal |journal=Nature |volume=321 |issue=6067s |pages=338–341 |date=15 May 1986 |doi=10.1038/321338a0 |bibcode = 1986Natur.321..338M |s2cid=122092751 }}</ref> for seven jets, and these caused the comet to wobble over long time periods.<ref name="esa" />

The dust ejected was mostly only the size of cigarette smoke particles, with [[Orders of magnitude (mass)|masses ranging from]] 10 ag to 0.4 g. (See [[Orders of magnitude (mass)]].) The mass of the particle that impacted ''Giotto'' and sent it spinning was not measured, but from its effects—it also probably broke off a piece of ''Giotto''<ref name="mcd" />—the mass has been estimated to lie between 0.1&nbsp;g and 1&nbsp;g.<ref name="esa" />

Two kinds of dust were seen: one with carbon, hydrogen, nitrogen and oxygen; the other with calcium, iron, magnesium, silicon and sodium.<ref name="esa" />

The ratio of abundances of the comet's light elements excluding nitrogen (i.e. hydrogen, carbon, oxygen) were the same as the Sun's. The implication is that the constituents of Halley are among the most primitive in the Solar System.

The plasma and ion mass spectrometer instruments showed Halley has a carbon-rich surface.

===Spacecraft achievements===

* ''Giotto'' made the closest approach to Halley's Comet and provided the best data for this comet.<ref name=Curdt_1988/>
* ''Giotto'' was the first spacecraft:
:* to provide detailed pictures of a cometary nucleus.<ref name=Keller_1986/>
:* to make a close flyby of two comets. Young and active comet [[Halley's Comet|Halley]] could be compared to old comet [[Grigg–Skjellerup]].
:* to return from interplanetary space and perform an Earth swing-by.
:* to be re-activated from hibernation mode.
:* to use Earth for a gravity assist.<ref name=beyond/>