Comet 9P/Tempel 1 was the target of a multi-wavelength worldwide investigation in 2005 .
The NASA Deep Impact mission reached the comet on 4.24 July 2005 , delivering a 370 kg impactor which hit the comet at 10.3 km s ^ { -1 } .
Following this impact , a cloud of gas and dust was excavated from the comet nucleus .
The comet was observed in 2005 prior to and after the impact , at 18-cm wavelength with the Nançay radio telescope , in the millimetre range with the IRAM and CSO radio telescopes , and at 557 GHz with the Odin satellite .

OH observations at Nançay provided a 4-month monitoring of the outgassing of the comet from March to June , followed by the observation of H _ { 2 } O with Odin from June to August 2005 .
The peak of outgassing was found to be around 1 \times 10 ^ { 28 } molec .
s ^ { -1 } between May and July .
Observations conducted with the IRAM 30-m radio telescope in May and July 2005 resulted in detections of HCN , CH _ { 3 } OH and H _ { 2 } S with classical abundances relative to water ( 0.12 , 2.7 and 0.5 % , respectively ) .
In addition , a variation of the HCN production rate with a period of 1.73 \pm 0.10 days was observed in May 2005 , consistent with the 1.7-day rotation period of the nucleus .
The phase of these variations , as well as those of CN seen in July by Jehin et al .
( 2006 ) , is consistent with a rotation period of the nucleus of 1.715 days and a strong variation of the outgassing activity by a factor 3 from minimum to maximum .
This also implies that the impact took place on the rising phase of the “ natural ” outgassing which reached its maximum \approx 4 h after the impact .

Post-impact observations at IRAM and CSO did not reveal a significant change of the outgassing rates and relative abundances , with the exception of CH _ { 3 } OH which may have been more abundant by up to one order of magnitude in the ejecta .
Most other variations are linked to the intrinsic variability of the comet .
The Odin satellite monitored nearly continuously the H _ { 2 } O line at 557 GHz during the 38 hours following the impact on the 4th of July , in addition to weekly monitoring .
Once the periodic variations related to the nucleus rotation are removed , a small increase of outgassing related to the impact is present , which corresponds to the release of \approx 5000 \pm 2000 tons of water .
Two other bursts of activity , also observed at other wavelengths , were seen on 23 June and 7 July ; they correspond to even larger releases of gas .