Why Do the Planets All Orbit the Sun in the Same Plane?

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The planets in our solar system all orbit the Sun in one shared plane. (Illustration by Dawn Yang)
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Q: Why do the planets all orbit the Sun in the same plane?

—Randi Eldevik | Stillwater, Oklahoma

Because of the way the Sun formed, explains David DeVorkin, a senior curator in the space history division at the Air and Space Museum. About 4.5 billion years ago, a massive cloud of dust started contracting as gravity pulled its parts toward the center. This dust cloud rotated slowly at first but sped up as it contracted, in much the same way that a figure skater spins more quickly when she pulls her arms closer to her body. (This law of physics, which makes things spin faster as they contract, is called angular momentum.) The faster rotation flattened the cloud into a pancake, with the Sun at the center and planets forming within that plane. Planetary systems around other stars tend to form in a similar way.

Q: Do male mammals lactate?

—J.T. Smith | Sway, England

Generally no, even though most male mammals have nipples, explains Michael Power, animal scientist at the National Zoo. In a mammalian embryo, nipples tend to form before the sex is determined, and since nipples serve little or no function in males, the process of evolution has not been under pressure to eliminate the vestigial feature over time. There are a few instances of lactating males, most notably the dayak fruit bats found in Southeast Asia. These bats produce a secretion from their nipples, but it’s unclear whether this substance, produced in small quantities, is capable of nourishing babies. As with other mammals, the females take sole responsibility for that.

Q: Since smoking is banned on almost all airlines, why are there still “No Smoking” signs above each row and ashtrays in airplane bathrooms?

—Eric Kim | Niagara Falls, New York

It’s more hassle than it’s worth to remove the signs from decades-old airplanes, explains Bob van der Linden, curator of air transportation at the Air and Space Museum: The process of getting Federal Aviation Administration approval to alter a commercial aircraft cabin is cumbersome. And though smoking has been prohibited on all major airlines since 2000, the agency still requires an ashtray in the lavatory as a safety measure because some passengers persist in trying to light up in secret. In one notorious instance, a 2013 flight from Nova Scotia to the Dominican Republic had to make an emergency stop in Bermuda when an entire family was caught smoking in a lavatory.

Q: How long does it take for a flower to replenish its nectar supply?

—Angela Taylor | Flat Rock, North Carolina

It all depends on the creature the flower evolved to attract, says Gary Krupnick, the head of the plant conservation unit at the Museum of Natural History. Nectar is a sugar-based substance that lures pollinators so their bodies transfer bits of fertilizing pollen from flower to flower. Plants adjust their nectar production to match the needs of their pollinators. Small blue borage flowers, which attract bees and butterflies, can replenish their nectar in two minutes. Agave plants, which attract needle-nosed bats, produce nectar only at night. A recent study found that evening primrose is even able to detect the specific sound frequencies of its bee pollinators. When it does, it produces fresh nectar in three minutes to attract them.

It’s your turn to Ask Smithsonian.

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