WASHINGTON • A little "Guardian of the Galaxy" has warmed the hearts of netizens despite being unsuccessful in his job application at US space agency Nasa.

Nine-year-old Jack Davis had applied for the role of planetary protection officer, which Nasa is looking to fill.

The three- to five-year appointment, which pays between US$124,000 (S$169,000) and US$187,000 annually, involves ensuring the agency complies with standards for preventing biological contamination outside of earth, and safeguarding the planet's biosphere from any alien life.

In a letter to Nasa which was tweeted by the space agency on Saturday, Jack said he felt he was a good fit as "my sister says I am an alien" and that he has watched "almost all the space and alien movies I can see".

The tweet has so far been retweeted 12,960 times, and liked 39,519 times.

"I have also seen the show Marvel Agents Of Shield and hope to see the movie Men In Black," he added for good measure.

Jack also said he is "great at video games" and can learn to think like an alien since he is young.

Nasa's director of its Planetary Science Division, Dr James Green, replied to the fourth grader in a personally signed letter.

He acknowledged Jack's interest and explained the responsibilities of the appointment.

He told the boy to "study hard and do well in school", and hoped to see him at Nasa one day.