Fifth graders Hailey Bedell and Molly Uthoff of Sikeston have the answer. "My very excellent mother just served us nachos," the girls said in unison, of course, referring to Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The St. Francis Xavier School students modified the original mnemonic device they learned -- "My very excellent mother just served us nine pizzas" -- to fit changes made Thursday by the International Astronomical Union, which officially stripped Pluto of the planetary status it has held since its discovery in 1930.
As word of the change spread throughout the education community Friday, teachers and students reacted to the news.
"It's going to immediately make all of our science books archaic," said Christy Priday, Sikeston R-6 elementary Eagle teacher.
Teachers will typically pull supplemental materials to teach students, and that's what they will have to do to teach about the solar system, Priday said.
"I think this is a good teaching strategy for science -- that people are always investigating and learning -- and now there will be an actual criteria to identify the planets," said Priday who, prior to this year, taught fourth grade for 10 years.
The decision by the prestigious international group of leading astronomers spells out the basic tests that celestial objects will have to meet before they can be considered for admission to the elite cosmic club.
For now, membership will be restricted to the eight ''classical'' planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Much-maligned Pluto -- named for the God of the underworld -- doesn't make the grade under the new rules for a planet: ''a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit.''
Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.
Instead, it will be reclassified in a new category of ''dwarf planets,'' similar to what long have been termed ''minor planets.'' The definition also lays out a third class of lesser objects that orbit the sun -- ''small solar system bodies,'' a term that will apply to numerous asteroids, comets and other natural satellites.
"I'd be sad if I was Pluto because I wouldn't be a planet anymore," Hailey said about Pluto being demoted to a "dwarf planet."
Sixth grader Matt Frazier said he's amazed Pluto isn't a planet anymore either.
"I think it's confusing," fifth grader Gavin O'Brien said. "They'll have to redo the science books."
Hailey agreed the concept is confusing. "Yesterday it was a planet, and today's it's not," she said.
The students then predicted 20 years from now it will be changed back into a planet.
Typically the solar system is introduced in second and third grades but gets more in depth in fourth grade, Priday said.
"I think this is exciting for science," Priday said. "I think it's good for kids to know learning is an ongoing process for all, and the world is ever changing and we need to keep our minds open to what's new out there."
Priday said she anticipates educators will have to come up with new strategies to teach about the different levels and categories of the planets and other celestial bodies.
But the hardest thing for people will be to change, Priday said.
"The experts make these decisions, obviously, but it's us changing our ideas about what we believe and what we think. This is something we've learned and now we will have to unlearn it," Priday said.
Just like people have counted on the sun to come up every morning and the seasons, they've counted on the solar system, Priday said.
"Even though it's not concrete to us -- it is a concept we've all grown up with, and it may be difficult for adults to accept and to allow their children to learn the new," Priday said.
Chad King, earth science instructor at Sikeston High School, said he doesn't understand why the astronomers wanted to change the status of Pluto.
"It was a major discovery in 1930, and now -- 76 years later -- it's not big enough to represent a planet," King said.
King noted the width around Pluto is just under 1,500 miles -- from Jefferson City to Los Angeles.
"For years, it's been fine," King said. "Why change it now?"
Shelly McSpadden, who works at Sikeston High School, couldn't agree more.
"Pluto will remain a planet amongst those of us who grew up knowing it as a planet," she said.
The Associated Press contributed to this article.