| OORTCLOUD | Could root out the origin of comets |
| OORT | Astronomer who proposed what is now the generally accepted model for the origin of comets (4) |
| ANNULI | Wipe out the origin of illicit rings (6) |
| HARROW | School that should root out the weeds? |
| FOP | Dandy to root out the rooftop (3) |
| PATHOGENESIS | As the GP, one is working out the origin and development of a disease (12) |
| TORSO | Roots out the trunk (5) |
| WEEDS | Roots out the black clothes (5) |
| TAILS | Evening dress including a morning coat of the same name; said cutaway's skirts; or, the caudae of horses or other beasts, thus braids, catkins, trains of comets or other long pendant things, suggestiv |
| HALLEY | "A Synopsis of the Astronomy of Comets" author |
| DONATI | Giovanni Battista ?, 19th-century Italian astronomer who pioneered the spectroscopy of comets (6) |
| ORT | O, almost a cloud of comets |
| BILLHALEY | Leader of comets alphabetically in disarray, disregarding a pact (4,5) |
| CUPID | Teammate of comet putting target on source of desires (5) |
| ROSETTA | Ancient stone picked up on tail of comet reflecting indication of position in space (7) |
| COMMEMORATE | To preserve the memory of comet, am more necessary to it (11) |
| NUCLEUS | Terrible Sun clue for part of comet's head |
| OCCULTS | Old sects screening head of comet's eclipses (7) |
| LACTOMETER | One used to measure density of comet moving in afterwards |
| TOTEMIC | Representation of comet, it is symbolic |
